failed: Cached message size smaller than expected

@lbutlr kremels at
Wed Apr 21 22:42:39 EEST 2021

On 21 Apr 2021, at 11:31, Michael Grant <mgrant at> wrote:
>>>> We don't really fix issues with mbox files anymore, other than read issues.. Our focus is enabling people to move to other formats, such as maildir. I would strongly recommend you to consider using maildir instead of mbox.
> Ugh, so many people still have their mail in mbox that I find it hard to believe this is "deprecated".

It's a terrible format and was developed when most people had mail that maybe took up several kilobytes of space.

>>>> I would also recommend you use dovecot-lda in procmail to deliver mail, if you are not already doing so.
> I wasn't, so it took me a couple days to try this and wait for it to
> happen again.  It's still happening.  I therefore think this probably
> doesn't have anything todo with procmail.

Procmail is old, creaky, has several known bugs, and is unmaintained. But also works perfectly well with Maildir, a vast improvement over mbox.

> You'll get a lot of pushback if you do this!  I'm not the only one
> using it.

Yeah, stirring gigabytes of mail in a single flat text file is a fantastic idea, I can see why some people are so hesitant to give it up.

Honestly, it's bad. Don't use it. 

> mailx and the gnu mail tools use it and I don't know if I
> can so easily migrate things to maildir format.

GNU Mail certainly can. You will be hard pressed to find a mail client that doesn't. (I've never used mail, but I would be surprised if it was mbox only). From the command line I only use mutt anymore.

> I think it could be a nightmare migrating to maildir.

It is not. In fact, it is a facility that is basically built in to formail (that's procmail's formail) which I think is in the formail man page (But it's been a few years since I stopped using procmail). There is also a utility.


> I seem to be or may be the only one on this server seeing the issue.
> I am also a heavy imap user.

mbox and IMAP together are a big bag of hurt. I switched from mbox back around 2000 specifically because of moving too IMAP.

> Is there any way 2 separate IMAP clients talking to dovecot could
> cause this?

With mbox files? I would sure think so. You have two processes potentially accessing the same file. That is never good.

> I'm really hoping that this is just some config issue.

It is, just not the config issue you think it is.


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