Bcc messages are not delivered to all recipients

[franciscodavid]

Hi,

I noticed a strange behavior in DavMail while sending a mail to a list of 10-15 bcc addresses. Apparently the mail is received by few recipients (from 1 to 3) but all the others don't get the mail, and it is impossible to know which one was not send if you don't look at DavMail's log.

In the logfile there are a some messages like the one below

DEBUG [SmtpConnection-34403] davmail.exchange.ExchangeSession - Dropping message id <[email protected]>: already sent

And then I can traceback which mail addresses were not delivered based on the connection port.

DEBUG [SmtpConnection-34403] davmail - < RCPT TO:<[email protected]>

I'm using DavMail as an SMTP proxy to send mails from the Gmail interface through an Office365 account.

My first impression is that Gmail is trying to send individually each copy of the mail, but uses the same message ID, which causes the problem in DavMail at this point.

I'm not sure if this is a bug or a non-standard behavior in Gmail's side. Here is a question related to message IDs and bcc in StackOverflow.

[franciscodavid]

Here is a proposal to fix this. I've been testing it for some days and seems to work without issues.