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Is it possible to configure options on email server containing Postfix and Dovecot, features similar to Gmail settings:

  1. Enable POP for all mail (even mail that's already been downloaded)

  2. Enable POP for mail that arrives from now on

I looked a lot at Google, but was unsuccessful. So if anyone has an idea, I would appreciate that.

Khaled
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driftux
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2 Answers2

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Your troubles at finding an answer are due to not looking at the right scope.

The option as to which email to download is a feature of a POP client, not the POP server. A POP server is to simply provide all email for a given user; the client can then decide to download all messages or ones selectively.

POP was developed when disk space and bandwidth were at a premium; once mail is downloaded from the server to the client, it is typically deleted (unless the client is configured otherwise).

What about using IMAP instead? You get the flexibility of that mail being available on multiple machines, and you conserve bandwidth by only downloading the headers of all messages and then only downloading message bodies of those messages actually being viewed. Then, when a message is deleted at the client, it can be marked as deleted at the server.

Rob Gibson
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  • Yes all information is known for me. I'm looking to use functions above. Gmail has these functions. For example user configured POP email account on computer A. He downloaded 10 messages. Then he went to computer B and configured the same email account. Computer B does not redownload 10 messages while user not checked "Enable POP for all mail (even mail that's already been downloaded)" Gmail has this feature. Zimbra also has this feature, and as far as I know Zimbra is based on Postfix. – driftux Jan 05 '13 at 18:21
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    You are confusing the server and client. In Gmail and Zimbra, the interface you use is the client, whereas Postfix is the SMTP server used to transfer mail back and forth. Dovecot is the tool doing POP. As far as the test messages, Computer A's POP client (Thunderbird/etc) is not configured to keep messages on the server. Since it is not, then the messages are downloaded to Computer A and then deleted from the POP server. When Computer B tries to connect, it does download all messages already downloaded (which is now none). Check the configuration of your *clients* very carefully. – Rob Gibson Jan 05 '13 at 18:29
  • @RobGibson GMail indeed has server side message filtering for POP and IMAP. I've never seen these features in an open-source mail server, and they seem completely useless. – Chris S Jan 05 '13 at 19:36
  • The filtering in Gmail is not "server-side". It is client-side filtering on a client in the cloud. In fact, it is a modified IMAP client hosted in the cloud, as the client-side filters defined in the web interface are used to modify the incoming messages, including spam filtering and adding tags. It's a subtle difference, but a critical one. No open-source mail server supports these options directly. Gmail, as I mentioned, is using client-side filters. Zimbra uses spamassassin and other tools to do server-side spam/virus filtering and client side filtering otherwise. – Rob Gibson Jan 05 '13 at 19:43
  • I'm taking just about POP, IMAP is not an option. So computer A has a GMAIL account with POP and option set "Leave a copy of the messages on the server" set. Computer A gets 10 emails and also leave messages on the server (user can see them through outlook and gmail webmail interface). If we configure computer B with the same Gmail account, it gets no messages to Outlook. Because Gmail "knows" that these messages was already sent to computer A account. ... – driftux Jan 05 '13 at 20:22
  • ... The only way to allow computer B redownload messages is to go GMAIL web interface settings and set option "Enable POP for all mail (even mail that's already been downloaded)". How does gmail implement such features? I would like to do so also with my email server. – driftux Jan 05 '13 at 20:23
  • Gmail implements their service as a modified IMAP server and client combination. POP does not inherently offer this feature on the server side. The two ways to allow computer B to download all of the messages on any other mail server are: 1. Tell Computer A's client to not delete messages from the server when retrieving them, usually labelled as "Keep a copy of the messages on the server". 2. Switch to using IMAP which is designed for allowing multiple clients to access the same message store in the way you describe. – Rob Gibson Jan 05 '13 at 20:51
  • I must use POP with option "Leave a copy of message on the server". Thats waht my users want. So Gmail POP act as modified IMAP? Does anyone knows more how gmail handles that? – driftux Jan 05 '13 at 21:17
  • I am quite curious, but why is IMAP not an option? – Rob Gibson Jan 05 '13 at 21:25
  • Because all my users want to have their email messages in Outlook even then internet connection is not possible. Also looking from the server resourses POP is not so hungry as IMAP. – driftux Jan 05 '13 at 21:49
  • With IMAP, not only do you get the benefits of seeing messages on multiple machines, but you can also configure Outlook, or any IMAP client, to cache new messages locally, providing the same offline capability as POP. Also, Zimbra has an addon available in their Network Edition (designed for production use and available with telephone support) which is an Outlook connector and makes the Zimbra server appear as a MAPI server to Outlook. You can then cache messages for offline use as your would an Exchange server. – Rob Gibson Jan 05 '13 at 23:04
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You can easily configure Dovecot to act as a POP3 server. Simply add the protocols to the Dovecot configuration file. For example:

protocols = imap imaps pop3 pop3s
Michael Hampton
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