transfering to another mailserver

Most free Business email hosting is gone. Even Gmail's free to micro-businesses is no longer available.

Assuming you want IMAP email, Gmail may still be a good hosting provider -- not because their mail is any better or worse than anyone else's, but because the "extras" that come with the other Google Apps is worth it (like sharing contacts and calendars with your smart phones being a snap!).

Most hosting providers (like GoDaddy and 1and1 offer low-cost POP mail services, but I don't recommend POP... not even for personal mail!

In case you don't know the difference, the design of POP & IMAP are different, and although you can change any number of settings, by default:
 - POP (Post Office Protocol) was designed for ISPs. The idea is that you connect to the server (with your Outlook Express client) and download your messages to your (one) computer. Once downloaded, the message is deleted from the server.
 - IMAP (Internet Message Access Protocol) was designed to replace POP. The fundamental difference being that messages "live" on the server, and clients (like Outlook, Thunderbird, iMail, iPhones, and Androids) "synchronize" with the server. Then, when you read a message on one client (and it re-syncs) the message is marked as READ on the server, and any other client that connects will see that said message has already been read. IMAP deals a little awkwardly with deletions -- messages are MARKED for deletion, and only actually removed when "purged".

Businesses, and most people with more than 1 device (computer, laptop, phone, etc) strongly prefer IMAP. POP is really only for people who don't know any better. (In my opinion).

NOTE: While you can tell a POP server not to delete messages just because they're downloaded, POP servers do NOT maintain message status, like READ, REPLIED TO, FORWARDED, or even MARKED FOR DELETION.

So back to how to move...
 - STEP 0: If you KNOW you're going to move in the future, set the TTL value on your MX records in DNS to something very low (like 900 -- or 15 minutes). This will eliminate the long-term caching of OLD values.
 - STEP 1: Create the new mail accounts (Gmail or elsewhere)
 - STEP 2: Validate that you can SEND mail FROM the accounts (you won't be able to send TO the accounts until DNS is fixed -- except for within your own domain and users on the NEW system).
 - STEP 3: Modify the MX records in your DNS to point to the new service. KEEP THE OLD MX RECORDS, just set their priority to a HIGHER number than for your new service. (That way, if there is a problem, the messages will fall thru to the old service)
 - STEP 4: Modify the SPF records (if any) on your DNS service to allow sending FROM the new addresses (this may not be necessary if your SPF is something simple like "a mx ~all" or the like.). If you don't HAVE SPF, you should add it as part of your migration.
 - STEP 5: Configure your clients to connect to the NEW service IN ADDITION to the OLD service.
 - STEP 6: Wait a day or so and make sure ALL USERS are receiving mail in the new service.
 - STEP 7: Tell your users to move any data from the OLD service into the NEW service. That means moving messages from the old Inbox to the new Inbox, as well as any folders. NOTE: As an alternative, users could move those messages into local storage, or an Archive location. Just remember, if you're migrating away from an IMAP service, once the service goes away, so does your access to your old mail/folders!
 - STEP 8: When users have moved all data off of the old server, remove the MX records from your DNS server & set the TTL back to a reasonable value (86400 is 1-day).
 - STEP 9: Deactivate your old mail accounts & remove the old mail settings from your client(s).

I know this sounds like a lot, but by accomplishing each step in order, you'll have an extremely easy transition and NOT leave yourself open to lost mail in the process.

CAVEAT: If you weren't able to set the TTL values low at least a couple of days BEFORE you started your change, let the new DNS settings (STEP 3) be in place for AT LEAST 3 DAYS before deactivating the old server or removing the settings.

I hope this helps!

Dan
IT4SOHO

Tell your users to move any data from the OLD service into the NEW service. That means moving messages from the old Inbox to the new Inbox, as well as any folders.

This seems like the most difficult step. Do you have examples.

If your users are using Outlook, they'll just drag and drop from their old mail location to the new one. Likewise if they're using Thunderbird.

It is somewhat harder if their only access is via web portal or mobile device.

Thunderbird is a tool I use to do this for clients with very VERY few users. Assuming we're going FROM IMAP TO IMAP, I can create both accounts in Thunderbird, then drag and drop between them.

NOTE: I usually don't even have to tell users to move the data from one account to the other. Once I tell them about how to connect to their new account -- and they see data starting to appear in that new account -- most users just start moving the data on their own.

Naturally, there are some who need a lot of hand-holding... but that's to be expected. You're dealing with end-users, and even a group of scientist end-users (my condition) still has a few who just can't seem to fathom the simplest things.

Hoping this is useful.

Dan
IT4SOHO

Thunderbird is a tool I use to do this for clients with very VERY few users. Assuming we're going FROM IMAP TO IMAP, I can create both accounts in Thunderbird, then drag and drop between them.

Will the result only show on my one desktop computer?

Or will I be able to see all the mail on every login after the drag and drop

The point of an IMAP service is that the "master copy" of your mail stays on the server (the IMAP server).
So, when you make changes to the IMAP account on a client -- and that client then synchronizes to the IMAP server, the changes are propagated to any other clients.

For example -- say you have a user who is a total NOOB with computers, and needs everything done for them:
 - First, I would change their email client (Thunderbird?) to use only the NEW email (for both IMAP and SMTP -- be careful of the latter, as in Thunderbird it is listed separately!!) I would tell the user to be patient about his old e-mails, they'll appear automatically (which is what I'll show you below).
 - Then, on my own system, I install the client's old IMAP server settings into Thunderbird, as well as the NEW settings.
 - I can drag the old messages OUT of the old IMAP server and INTO the new server... and as it progresses, each time the NOOB user resynchronizes to the IMAP server, more and more messages will appear.
 - The only CAVEAT is that migrated folders won't appear until someone actually adds the folders in the client on the NOOB user's system.

I don't recommend doing this for large numbers of users -- most users can figure this out themselves: with both IMAP servers installed, move the mail from the old one to the new one, then uninstall the old service.

I hope this helps explain what you wanted...

Dan
IT4SOHO

are emails all saved as .eml files

Message formatting -- whether on the local computer, or on the mail server -- should be immaterial to the concept of moving mail services (servers).

You will use IMAP (or, choke, POP) to access the files on the server -- so whether the server uses an mbox or maildir (or even exchange DB) format on the server... it won't matter to you. The "response" (or "download") of the message will be the same (in the IMAP... or pop... format).

You will presumably be using the same program as a client (whether Outlook, Thunderbird, iMail, Opera, etc) for each of the 2 mail services, so what format the client uses to store the messages (.eml is typical for an ATTACHED message in Outlook) is equally immaterial.

One thing to note with Outlook 2013 and IMAP: It is just one of very MANY ways MS screwed up Outlook in 2013, but the IMAP messages in 2013 are stored in an OST file (vs. PST for every previous version of Outlook). This means that you CANNOT move the local storage file (OST) over to the new IMAP server. You would need to export into a PST, then re-import to the "new" OST file.

Personally, I like the way Thunderbird does things -- it's a simple sync of the "subscribed" folders -- thus, no unintentional overcooking of the soup.

Dan
IT4SOHO

The "response" (or "download") of the message will be the same (in the IMAP... or pop... format).

So is each message a response or file?

Thanks for mail explanation