The lmtp runner doesn't accept messages to addresses with local parts exceeding 64 bytes.

This is a restriction in aiosmtpd. I have filed https://github.com/aio-libs/aiosmtpd/issues/257 for that, but in the mean time before this is fixed there, if it will be fixed there, we need some kind of workaround. This issue causes confirmations addressed to LISTNAME-confirm-TOKEN@example.com to be rejected if LISTNAME is longer than 15 bytes since TOKEN is 40 bytes.