[Dovecot] Thunderbird 1.5 and dovecot 1.0 beta 3 problem

[Peterg]

My mailhosting provider has been testing dovecot 1.0 beta 3 as a proxy server
and they asked the customers if they would like to test it out and report any
issues. I am using Thunderbird 1.5 (IMAP) and have been with this mailhosting
company for two months and have no issues at all with their current setup which
uses Perdition as their proxy servers.

The problem(s) I am encountered have been reported here a few times previously
over the last couple of years but in searching I have not found any concrete
solutions. When I first tested it out there was a continuous problem of a
failure in saving a copy of an email to the sent folder although the message was
sent. One of the staff of the mailhosting company noted this exact problem as
well and believed the issue was Dovecot announcing different IMAP capabilities
than the real backend IMAP servers (via the CAPABILITY command). This was
supposedly fixed and initially there were no issues with the first set of test
emails. However, in short order, this problem re-emerged and there would be
sporadic failures to copy a message to the sent folder. Another issue would be
that every now and then, when clicking on a folder in the left-hand pane (and no
other activity going on with Thunderbird like downloading a new mail)
Thunderbird would hourglass for 10-15 seconds as if it were trying to open a
connection and was having difficulty. The maximum number of connections setup in
Thunderbird is the default 5 and I am advised that this is the correct setting
with their servers. Reducing the maximum number of connections does not appear
to change matters in terms of avoiding these problems.

Changing back to the current system (ie not using the test proxy server) both
these issues disappeared. I have been in communication with the mailhosting
provider as to my findings but it would be most appreciated if others here would
perhaps have some insight into this matter. 

Peter