Self-explanatory, I hope (note the period on the end of the username); sieve/pigeonhole does not allow you to have senders which end with a period, which means that any UNIX users with such usernames who send mail have it rejected by sieve:
# useradd testuser. # su - testuser. $ mail david@example.com -s 'testing' 123 . [testuser.@levi ~]$ logout
# less /var/log/maillog
Aug 22 07:50:56 levi dovecot: lda(david@example.com): Error: sieve: envelope sender address 'testuser.@myhost.example.com' is unparsable
Versions: dovecot-pigeonhole-0.2.6-21.el5 dovecot-managesieve-0.2.6-21.el5 dovecot-2.0.18-1_134.el5
Why would anyone have a UNIX username ending in a period? For one, web hosting companies may use your domain name as your username - but be subject to a 32-character limit, so your domain name gets truncated.
David
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