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Transferring mail to a new mail server

© January 2005 Tony Lawrence

Sometimes we just have to move on. Your current mail server may just not be meeting your needs, so you've put up something new. But what about old mail? If your servers are identical (Sendmail to Sendmail, etc.) or use the same mailbox storage format, you may be able to just transfer files directly. If not, read on..

If everyone uses POP, there's usually not much to transfer, and if you can shut off incoming mail and just wait long enough for everyone to pop their mail, there won't be anything. But many people now use IMAP.

It's actually sometime useful NOT to transfer anything. Many users let their mailboxes build up without ever deleting unneeded messages. If you can leave the old server on the network, they can always access their old mail if they need to, but they (and you) may find after a year or so that nobody ever has. You might then archive the messages "Just in case" and take down the old server.

If you do want to transfer messages, it can be as simple as running command line tools. The first thing to do is to set the old server to forward all mail to the new server. Exactly what you do to accomplish that depends on your server, but it should be easy. For sendmail, you'd set SMART_HOST and MAIL_HUB, or edit the aliases file and forward each user. For SME server, set the "Delegate Mail Server" in the Server Manager.

Transferring existing mail depends on the format it now uses. For example, Qmail stores messages in individual files. On an SME server (which uses Qmail) you could transfer "tony"'s current mail with just this:

cd /home/e-smith/files/users/tony/Maildir
for i in *
 cat $i | /var/qmail/bin/qmail-inject

Repeating that for each directory would move all mail to the new server. However, it all ends up in the user's INBOX unless that server can apply rules to determine where to file it. To assist that, you may want to use a perl program instead. Something like this:

use Mail::Mailer;

foreach (@stuff) {
    $from=$_ if /^From:/;
    $to=$_ if /^To:/;
    $subject=$_ if /^Subject:/;
    last if $subject;
$from=~ s/From: //;
$from=~ s/<//;
$from=~ s/>//;
$to=~ s/To: //;
$to=~ s/<//;
$to=~ s/>//;
$subject=~ s/^/*** FILE ME IN CUSTS ***/;
$mailer->open({From =>$from,
               To => $to,
               Subject => $subject,
           }) or die "Can't open $!\n";
foreach (@stuff) {
    print $mailer $_;

You'd adjust the modification to Subject appropriately, or add entirely new headers if desired.

If your mail is stored in Unix mailbox fashion, you need something to read the messages and break them up. While you could read the mailboxes directly, it's more portable to use tools like POP:

use Net::POP3;
$pop=Net::POP3->new('') or die "$!";
foreach $msg(keys %$messages) {
  foreach (@$message) {
    #same basic idea as above, 

You may need to get Net::POP3 from CPAN. There are similar modules for IMAP.

Bruce Garlock suggested that Mailsync might also be useful here.

Got something to add? Send me email.

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-> Transferring mail to a new mail server

Inexpensive and informative Apple related e-books:

Take Control of OS X Server

El Capitan: A Take Control Crash Course

Digital Sharing Crash Course

Take Control of Upgrading to El Capitan

Take Control of iCloud

More Articles by © Tony Lawrence

---January 11, 2005

I wonder if mailsync; https://mailsync.sourceforge.net/ could be used to do this as well. It looks like it could be another option for transferring a mailbox to a new machine.


---January 11, 2005

Yes, looks like it could - thanks!


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