Comment 5 for bug 1633220

@ChristianEhrhardt - Yes, it is sure that dovecot panics for e-mails of this size.
We encountered the issue with e-mails which are a few kilobytes smaller, but the exact threshold
might vary (e.g. depending on 'server speed').
All in all 60K seems to be the right magnitude.
I would also like to mention that the bug occurs independent of the executed filter.
A simple filter that would read the mail from stdin and pass it to stdout without any modification would be sufficient to trigger the described behavior.

We could verify a fix / a newer version against our setup in Xenial and Yakkety.