How to debug email sending issues? (some recipients don't get some emails)

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AI-generated summary

sjjh reports an issue where some users fail to receive emails in mailing list mode, with no corresponding entries found in the admin email protocol logs (not even in skipped or bounced). merefield asks if the instance is hosted and suggests checking provider logs, but confirms that if it is self-hosted, the absence of a log entry implies the email was never queued for sending.

To identify why emails might be suppressed, merefield provided a summary of conditions from the codebase where delivery is skipped in mailing list mode. These include: user muting topics/categories/tags, ignoring the author, lack of access to the post, inactive/suspended accounts, excluding their own posts, deletion of content, or high bounce scores.

sjjh meticulously checked each of these conditions against a specific affected user but found that none of them applied. Despite ruling out all known suppression reasons, the email was still not generated or logged. sjjh expressed concern over the impact on user trust and requested further debugging advice to identify the root cause of these random missing emails.

1

Some users report, that they don’t get some emails from our discourse instance. We are using “mailing list mode”. I tried to analyze one specific occurrence: approximately four out of 117 users of a group reported that they did not get a given mail. The other people did get the email. The affected users did get other emails from the same category (before and after the affected mail). Looking at the admin panel > email protocol, I can filter for the email address of an affected user and do not see an entry for the given post/email, either in the tab sent, nor in skipped or bounced.
How can I debug further what the root cause might be?

Maybe related (open/no cause found): Weird behaviour for sent emails

2

Are you hosted? Talk to your host.

If self-hosted, who is your email sending provider? Have you looked at your logs there?

3

self hosted. Shouldn’t I see the email as mentioned in the mail protocol under sent, if it was forwarded to our email provider (it’s Strato)?

4

Yes that is true.

I used a coding agent to summarise when emails are suppressed in mailing list mode:

- The user muted the topic, category, or one of its tags.
- The user muted or ignored the author.
- The user cannot access the post - for example, it is in a restricted category.
- The account is inactive, silenced, suspended, or awaiting required approval.
- The user chose to exclude their own posts.
- The post or topic was deleted before delivery.
- Previous delivery failures pushed the user’s bounce score over the configured threshold.

but you can look at the code yourself:

5

Thanks, as an admin I mocked the user and I’ll go to each of it to debug the case:

  • General: mailing list mode is activated in the user settings (via global setting)
  • the topic is not muted (in topic view)
  • no category is muted (in user settings)
  • the topic does not use any tag (in topic view)
  • no user is muted (in user settings)
  • the user can access the post
  • the account is not inactive, silenced, suspended, or awaiting required approval
  • the post is from a different user
  • the post (and topic) is not deleted
  • the user received an email to another topic on the same day, thus the bounce score seems not have been active.

So what else can it be? How can I debug the issue further? I’m a little lost… :-/

6

Anyone else having an idea? Random lost emails erode users trust in the system, and I’d like to improve stability here.
@Falco sorry for pinging you directly. As you were involved in the discussion of above topic covering an issue with the same effect, maybe do you have another pointer to dig deeper? Hope it’s not some rare 5 year old bug… :slight_smile: