It seems the bounce system isn't catching / logging all the bounces. I sent out a pc to all 1800 members this morning. So far, I have received 87 bounced email notices, but the log only shows 7 entries.
Has the situation changed at all since posting this thread?
This is potentially expected to a point. The EmailBounce process will run via Cron entry every 30 minutes, and when it does run it will only run for a maximum of X seconds (probably around 8 seconds or so).
Depending on how quickly the process is running, I could see it taking a few runs before catching everything.
However, if the log entries aren't growing at all and there's still a fair few missing this could be indicating some other issue.
How are you determining there are bounce entries missed? If you're accessing the account, you may be making them unavailable to XF to process (either because they're not available via POP3 or because they're not considered new via IMAP). In general, you won't want to access the account if there are pending messages (though the specifics will vary based on your mail server).
The bounce log will include every email it reads, even if it can't find relevant details. So if you're not checking the account, that would potentially imply an issue reading the account or an error (a fatal one?) when reading the messages. I assume there are no server error logs in XF, so an error would have to either be a fatal PHP error or something killing the process.
Depends on when the account was checked in XF vs when your client may have checked it, variations depending on whether messages were read, etc.
Note that you need to be using a dedicated account that only handles email bounces so XF can be the sole source checking it. (If you're using IMAP, you may be able to get away with looking at messages processed by XF already, but I wouldn't do that until any issues were confirmed to be resolved.)
Maybe they were picked up before they were downloaded to your email client.
Ultimately the best thing to do is to have bounces going into a completely separate mailbox. It may be OK to access the mailbox directly (e.g. I can't be certain but I'm pretty sure accessing a mailbox via webmail should be ok as long as the mails remain unread), but downloading them in any way is potentially going to either remove them from the mailbox or mark them in such a way that the bounce processor would ignore them.
You could set up a limited test to confirm it is working.
Set up a test user with a fake email that has a fake non existent domain.
Send them a Conversation.
Download the bounces to your client.
Does the bounce get processed by XF? I'm guessing not.
Second test, close your client and any other clients that may access that mailbox. Send another conversation.
Run the Email bounce Cron in Tools > Cron Entry.
Does the bounce get processed? At this point I'm presuming yes.
If the theory is wrong there may be some other issue but that test seems fair right now.