I've slowly become aware that quite a lot of email sent to me hasn't arrived. Some does and some doesn't. I can't say for sure how much but I'm starting to think 50% or more is getting lost. The sender does not receive any notification so neither side knows it was lost.

I've asked my regular correspondents to copy any future mail to the problem account and to a working account so by comparing I can get an idea of the scale of the problem and will hopefully know when it's fixed.

I've tried various things but would like to know if there are any logging or debugging tools available. Ideally I'd like a list with one line for each email coming in, giving sender address, subject, date, time and an indication of how it was processed.

Are there any such tools I can install?

Thanks

Lucky you with just 10 spam a day. I get about 3,000! But most of these are to non-existent addresses on my domain so they're easy enough to filter out. I have a catchall/default address and leave the rest open in order to be able to generate other addresses easily without creating a new account on cPanel.

Shortly after my original post I changed the default address. It had been my main account (where I was losing mail) and I used filters to separate the spam from mail to legitimate addresses which gets redirected. Now I have a different account as default and I do user level filtering on that, leaving my main account for its own mail only. So far there've been no problems, based on people copying to another working account. But I've also stopped using my android phone for mail in case that was the problem (it started around the time I started using the phone for email). I'll restart using the phone when I'm really confident things are OK.

Because the spam to non-existent addreses is discarded silently (without notification) I wonder if it makes a target for spammers. Do they mail random addresses on a domain to see if they get a notification? If so, the problem now is that if I set up a notification email for non-existent addresses I'll be sending out 3,000 bounces every day to the poor people whose address is being spoofed. Or maybe all domains are being equally but invisibly hammered by spam to non-existent addresses.

Thanks Troy,
yes it is POP and yes I have been thinking about IMAP. But IMAP seems to be more of a server-based system and I've always just downloaded my mail to a client. I have Thunderbird on the PC and set it to leave mail on the server for two days so I can still download it to the phone if I've gone out with the PC left on. And the phone is set not to delete after downloading. It ought to work. In fact it did work and I've no proof that that's why I'm losing mail. That's why I was wondering if there's some sort of logging or debugging that I can enable to find out what's happening.

Thanks Troy. That would almost fit with the symptoms. The phone polls and wrongly deletes email from the server; at the next poll the email disappears from the phone because it's no longer on the server (that's how I have it configured). And of course the PC might miss the mail between its own polls. The only thing is that I would have expected to hear the email notification on the phone. It would be interesting to know exactly which OS and mail software shows this problem. It can't be all phones.

Unfortunately I rarely detect a lost email within 24 hours. At the moment it seems OK. I think that changing my main personal account not to be the catchall might have had an effect although if the filters are working OK it shouldn't make a difference.

I use a regex match to select To addresses.
It's a 'negative look-behind assertion' that says if you do NOT have any of these names immediately preceding @domain then it's a match to be discarded or rerouted. (It also matches longer name strings that end in name1, etc. but that suits my purposes.) It has always worked in the past but I wonder if it's CPU intensive and fails at times of high spam. It filters about 3,000 invalidly addressed spams each day.

Anyway, this filter is no longer applied to the account but just to the user which is the new catchall.