As noted in https://moodle.org/mod/forum/discuss.php?d=277594#p1244223, The message_inbound configuration is missing a check on the length of the localpart section.

As per the RFC, the localpart of an e-mail address must be no greater than 64 characters including any subaddress component. At the moment, this is not enforced, nor is it checked. If a longer address is specified, it is generated, but not used causing much confusion and consternation.