2 emails rejected by 2026.4.0-latest ( 5f0d95e1f1 )

April 7, 2026, 8:37pm 1

Hi, I’m seeing an intermittent inbound email processing failure on a self-hosted site using mail-receiver.

What happened

Two separate inbound emails:

were delivered to the correct Discourse address
appear in /admin/email/received
also appear in /admin/email/rejected
show the generic rejection text: “There was an unrecognised error whilst processing your email and it wasn’t posted.”

At around the same time, logs showed ActiveRecord::Deadlocked.

Why I think this may be a bug

I compared the rejected emails with a later successful email of a very similar format:

same sender pattern
same Microsoft / Power Automate path
same visible To: shape
same SMTP envelope recipient to the Discourse address

So this does not look like a simple configuration issue with mail-receiver.

Evidence

For both rejected emails:

they were separate deliveries with different Message-IDs
they had different Postfix queue ids
both were delivered for <ppyem3.accomodation@discourse.domain.com>

I also observed ActiveRecord::Deadlocked in logs around the same period.

Hosting context

self-hosted
using mail-receiver
small IONOS VPS
1 web worker configured

I realise the 1 web worker may just be background context rather than the cause, since this appears to be inbound email/background processing rather than web request handling.

If useful, I can provide:

redacted headers for the 2 rejected emails
redacted headers for a successful comparable email
the deadlock log entry

Ethsim2 (Ethan ) April 7, 2026, 9:12pm 2

browsing the /logs endpoint, i see the two errors

env

hostname	ubuntu-app
process_id	2297
application_version	5f0d95e1f11a9cb5acbe8c7a61142400fc506f06
job	Jobs::ProcessEmail
db	default
time	7:48 pm

backtrace

activesupport-8.0.5/lib/active_support/broadcast_logger.rb:218:in 'block in ActiveSupport::BroadcastLogger#dispatch' 
activesupport-8.0.5/lib/active_support/broadcast_logger.rb:217:in 'Array#map' 
activesupport-8.0.5/lib/active_support/broadcast_logger.rb:217:in 'ActiveSupport::BroadcastLogger#dispatch' 
activesupport-8.0.5/lib/active_support/broadcast_logger.rb:129:in 'ActiveSupport::BroadcastLogger#error' 
/var/www/discourse/lib/email/processor.rb:126:in 'Email::Processor#handle_failure' 
/var/www/discourse/lib/email/processor.rb:31:in 'Email::Processor#process!' 
/var/www/discourse/lib/email/processor.rb:13:in 'Email::Processor.process!' 
/var/www/discourse/app/jobs/regular/process_email.rb:8:in 'Jobs::ProcessEmail#execute' 
/var/www/discourse/app/jobs/base.rb:318:in 'block (2 levels) in Jobs::Base#perform' 
rails_multisite-7.0.0/lib/rails_multisite/connection_management/null_instance.rb:49:in 'RailsMultisite::ConnectionManagement::NullInstance#with_connection'
rails_multisite-7.0.0/lib/rails_multisite/connection_management.rb:17:in 'RailsMultisite::ConnectionManagement.with_connection'
/var/www/discourse/app/jobs/base.rb:305:in 'block in Jobs::Base#perform' 
/var/www/discourse/app/jobs/base.rb:301:in 'Array#each' 
/var/www/discourse/app/jobs/base.rb:301:in 'Jobs::Base#perform' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:220:in 'Sidekiq::Processor#execute_job' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:185:in 'block (4 levels) in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:180:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
/var/www/discourse/lib/sidekiq/suppress_user_email_errors.rb:6:in 'Sidekiq::SuppressUserEmailErrors#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
/var/www/discourse/lib/sidekiq/discourse_event.rb:6:in 'Sidekiq::DiscourseEvent#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
/var/www/discourse/lib/sidekiq/pausable.rb:131:in 'Sidekiq::Pausable#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/job/interrupt_handler.rb:9:in 'Sidekiq::Job::InterruptHandler#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/metrics/tracking.rb:26:in 'Sidekiq::Metrics::ExecutionTracker#track' 
sidekiq-7.3.10/lib/sidekiq/metrics/tracking.rb:134:in 'Sidekiq::Metrics::Middleware#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:173:in 'Sidekiq::Middleware::Chain#invoke' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:184:in 'block (3 levels) in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:145:in 'block (6 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_retry.rb:118:in 'Sidekiq::JobRetry#local' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:144:in 'block (5 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/config.rb:39:in 'block in <class:Config>' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:139:in 'block (4 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:281:in 'Sidekiq::Processor#stats' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:134:in 'block (3 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_logger.rb:15:in 'Sidekiq::JobLogger#call' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:133:in 'block (2 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_retry.rb:85:in 'Sidekiq::JobRetry#global' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:132:in 'block in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_logger.rb:40:in 'Sidekiq::JobLogger#prepare' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:131:in 'Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:183:in 'block (2 levels) in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:182:in 'Thread.handle_interrupt' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:182:in 'block in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:181:in 'Thread.handle_interrupt' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:181:in 'Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:86:in 'Sidekiq::Processor#process_one' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:76:in 'Sidekiq::Processor#run' 
sidekiq-7.3.10/lib/sidekiq/component.rb:10:in 'Sidekiq::Component#watchdog' 
sidekiq-7.3.10/lib/sidekiq/component.rb:19:in 'block in Sidekiq::Component#safe_thread'

info

Unrecognized error type (ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR:  deadlock detected
DETAIL:  Process 1170676 waits for ShareLock on transaction 3318694; blocked by process 1169876.
Process 1169876 waits for ExclusiveLock on tuple (4,27) of relation 74547 of database 16384; blocked by process 1170546.
Process 1170546 waits for ShareLock on transaction 3318690; blocked by process 1170676.
HINT:  See server log for query details.
CONTEXT:  while updating tuple (1,54) in relation "user_stats"
) when processing incoming email

Backtrace:
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/patches/db/pg/alias_method.rb:109:in 'PG::Connection#exec'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/patches/db/pg/alias_method.rb:109:in 'PG::Connection#async_exec'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:167:in 'ActiveRecord::ConnectionAdapters::PostgreSQL::DatabaseStatements#perform_query'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/abstract/database_statements.rb:556:in 'block (2 levels) in ActiveRecord::ConnectionAdapters::DatabaseStatements#raw_execute'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:1022:in 'block in ActiveRecord::ConnectionAdapters::AbstractAdapter#with_raw_connection'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activesupport-8.0.5/lib/active_support/concurrency/null_lock.rb:9:in 'ActiveSupport::Concurrency::NullLock#synchronize'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:991:in 'ActiveRecord::ConnectionAdapters::AbstractAdapter#with_raw_connection'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_ad...

env

hostname	ubuntu-app
process_id	2297
application_version	5f0d95e1f11a9cb5acbe8c7a61142400fc506f06
job	Jobs::ProcessEmail
db	default
time	7:48 pm

backtrace

activesupport-8.0.5/lib/active_support/broadcast_logger.rb:218:in 'block in ActiveSupport::BroadcastLogger#dispatch' 
activesupport-8.0.5/lib/active_support/broadcast_logger.rb:217:in 'Array#map' 
activesupport-8.0.5/lib/active_support/broadcast_logger.rb:217:in 'ActiveSupport::BroadcastLogger#dispatch' 
activesupport-8.0.5/lib/active_support/broadcast_logger.rb:129:in 'ActiveSupport::BroadcastLogger#error' 
/var/www/discourse/lib/email/processor.rb:126:in 'Email::Processor#handle_failure' 
/var/www/discourse/lib/email/processor.rb:31:in 'Email::Processor#process!' 
/var/www/discourse/lib/email/processor.rb:13:in 'Email::Processor.process!' 
/var/www/discourse/app/jobs/regular/process_email.rb:8:in 'Jobs::ProcessEmail#execute' 
/var/www/discourse/app/jobs/base.rb:318:in 'block (2 levels) in Jobs::Base#perform' 
rails_multisite-7.0.0/lib/rails_multisite/connection_management/null_instance.rb:49:in 'RailsMultisite::ConnectionManagement::NullInstance#with_connection'
rails_multisite-7.0.0/lib/rails_multisite/connection_management.rb:17:in 'RailsMultisite::ConnectionManagement.with_connection'
/var/www/discourse/app/jobs/base.rb:305:in 'block in Jobs::Base#perform' 
/var/www/discourse/app/jobs/base.rb:301:in 'Array#each' 
/var/www/discourse/app/jobs/base.rb:301:in 'Jobs::Base#perform' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:220:in 'Sidekiq::Processor#execute_job' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:185:in 'block (4 levels) in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:180:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
/var/www/discourse/lib/sidekiq/suppress_user_email_errors.rb:6:in 'Sidekiq::SuppressUserEmailErrors#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
/var/www/discourse/lib/sidekiq/discourse_event.rb:6:in 'Sidekiq::DiscourseEvent#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
/var/www/discourse/lib/sidekiq/pausable.rb:131:in 'Sidekiq::Pausable#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/job/interrupt_handler.rb:9:in 'Sidekiq::Job::InterruptHandler#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:183:in 'block in Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/metrics/tracking.rb:26:in 'Sidekiq::Metrics::ExecutionTracker#track' 
sidekiq-7.3.10/lib/sidekiq/metrics/tracking.rb:134:in 'Sidekiq::Metrics::Middleware#call' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:182:in 'Sidekiq::Middleware::Chain#traverse' 
sidekiq-7.3.10/lib/sidekiq/middleware/chain.rb:173:in 'Sidekiq::Middleware::Chain#invoke' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:184:in 'block (3 levels) in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:145:in 'block (6 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_retry.rb:118:in 'Sidekiq::JobRetry#local' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:144:in 'block (5 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/config.rb:39:in 'block in <class:Config>' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:139:in 'block (4 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:281:in 'Sidekiq::Processor#stats' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:134:in 'block (3 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_logger.rb:15:in 'Sidekiq::JobLogger#call' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:133:in 'block (2 levels) in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_retry.rb:85:in 'Sidekiq::JobRetry#global' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:132:in 'block in Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/job_logger.rb:40:in 'Sidekiq::JobLogger#prepare' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:131:in 'Sidekiq::Processor#dispatch' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:183:in 'block (2 levels) in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:182:in 'Thread.handle_interrupt' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:182:in 'block in Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:181:in 'Thread.handle_interrupt' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:181:in 'Sidekiq::Processor#process' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:86:in 'Sidekiq::Processor#process_one' 
sidekiq-7.3.10/lib/sidekiq/processor.rb:76:in 'Sidekiq::Processor#run' 
sidekiq-7.3.10/lib/sidekiq/component.rb:10:in 'Sidekiq::Component#watchdog' 
sidekiq-7.3.10/lib/sidekiq/component.rb:19:in 'block in Sidekiq::Component#safe_thread'

info

Unrecognized error type (ActiveRecord::Deadlocked: PG::TRDeadlockDetected: ERROR:  deadlock detected
DETAIL:  Process 1170678 waits for ShareLock on transaction 3318690; blocked by process 1170676.
Process 1170676 waits for ShareLock on transaction 3318694; blocked by process 1169876.
Process 1169876 waits for ExclusiveLock on tuple (4,27) of relation 74547 of database 16384; blocked by process 1170678.
HINT:  See server log for query details.
CONTEXT:  while locking tuple (4,27) in relation "categories"
) when processing incoming email

Backtrace:
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/patches/db/pg/alias_method.rb:109:in 'PG::Connection#exec'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/rack-mini-profiler-4.0.1/lib/patches/db/pg/alias_method.rb:109:in 'PG::Connection#async_exec'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/postgresql/database_statements.rb:167:in 'ActiveRecord::ConnectionAdapters::PostgreSQL::DatabaseStatements#perform_query'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/abstract/database_statements.rb:556:in 'block (2 levels) in ActiveRecord::ConnectionAdapters::DatabaseStatements#raw_execute'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:1022:in 'block in ActiveRecord::ConnectionAdapters::AbstractAdapter#with_raw_connection'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activesupport-8.0.5/lib/active_support/concurrency/null_lock.rb:9:in 'ActiveSupport::Concurrency::NullLock#synchronize'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_adapters/abstract_adapter.rb:991:in 'ActiveRecord::ConnectionAdapters::AbstractAdapter#with_raw_connection'
  /var/www/discourse/vendor/bundle/ruby/3.4.0/gems/activerecord-8.0.5/lib/active_record/connection_ada...

Ethsim2 (Ethan ) April 7, 2026, 9:37pm 3

Hi, thanks for taking a look - I want to make sure I gather the right additional data before running anything noisy on the server.

Based on the deadlock and how Jobs::ProcessEmail runs, I’m thinking the following might help narrow this down, but I’d appreciate confirmation before I proceed.

1. Email header comparison (failed vs successful)

I can extract and post redacted raw headers from:

/admin/email/received → “Show original”

For:

1 failed email

or both as per

1 successful email of the same pattern

as per

This would include:

Message-ID
From
To
Delivered-To
Return-Path
top Received: lines

Would that comparison be useful here?

2. Sidekiq job outcome (retry / dead set)

Since this is happening inside Jobs::ProcessEmail, I can check whether the jobs:

retried
eventually succeeded
or landed in the dead set

Using:

./launcher enter app
rails c
Sidekiq::RetrySet.new.select { |j| j.klass == "Jobs::ProcessEmail" }
Sidekiq::DeadSet.new.select { |j| j.klass == "Jobs::ProcessEmail" }

Would confirming the retry/dead-set behaviour help diagnose this?

Concurrency configuration

I mentioned I’m running with 1 web worker, but I realise Sidekiq concurrency is likely more relevant for a deadlock.

I can share the relevant values from app.yml, e.g.:

UNICORN_WORKERS:
SIDEKIQ_CONCURRENCY:

At the moment, I don’t have SIDEKIQ_CONCURRENCY explicitly set in app.yml, so I believe this is running with the default concurrency (i.e. multiple Sidekiq threads).

Would that be important context for interpreting the deadlock?

PostgreSQL version

Since this is a PG::TRDeadlockDetected, I can also confirm the exact PostgreSQL version in use.

Is that worth including?

Timing of inbound emails

I observed that the two failed emails were processed very close together in time (same minute).

I can extract more precise timing from logs if useful.

Would tighter timing correlation help confirm whether this is a concurrency-triggered issue?

If helpful, I can gather and post all of the above in a follow-up - just wanted to check what would be most useful first.

Thanks again

Ethsim2 (Ethan ) April 8, 2026, 8:32am 4

Might be worth mentioning that the day after, 12 manually-triggered emails were received with time range of ~8 minutes

Yesterday evening, 4 of these automated emails were received, likely with a time range less than 8 minutes

Ethsim2 (Ethan ) April 15, 2026, 8:26pm 5

i have since upgraded to the medium + IONOS VPS with twice as many cores and double memory.

 ## Set db_shared_buffers to a max of 25% of the tot>
 ## will be set automatically by bootstrap based on >
db_shared_buffers: "512MB"
 ## can improve sorting performance, but adds memory>
db_work_mem: "10MB"

 ## Which Git revision should this container use? (d>
 #version: tests-passed

upload_size: 20m

 #these API limits were changed based on https://met>

DISCOURSE_MAX_USER_API_REQS_PER_MINUTE: 40

DISCOURSE_MAX_USER_API_REQS_PER_DAY: 14560

DISCOURSE_MAX_ADMIN_API_REQS_PER_MINUTE: 130

 # end of changes due to the meta topic quoted above>

## How many concurrent web requests are supported? >
 ## will be set automatically by bootstrap based on >
UNICORN_WORKERS: 4
 ## TODO: The domain name this Discourse instance wi>
 ## Required. Discourse will not work with a bare IP>

i haven’t noticed any issues in the week of trialling this server, so i am fairly certain there is no bug/regression here.

When the server was too small, Postgres did what it should.

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