I am changing webhosts and will be using the new hosts mail servers instead of the old ones.
I have created all the correctly named mailboxes on the new service but have also not yet cut ties with the old webhost. I am expecting that even if the new DNS values which point to the new hosts DNS servers and respective SOA\zone file with the new MX values have not yet propagated and an E-mail is directed at the old hosts mail servers as per the mx records in the SOA\zone records which the old hosting provider holds, the E-mail would still come through to the mailbox that's on the old host providers mail servers. So I am just trying to reaffirm if I got this right and it's essentially impossible for me to loose an E-mail since it will hit either the old hosts mail servers or the new ones ?
Also is it possible to configure the same E-mail account to check and collect mail from different mail servers by entering multiple pop3 addresses ? And if I choose to keep the old web hosts mail hosting services as a backup by specifying the mx records for it with a lower priority in the SOA records hosted by the new webhost, is it possible to have any incoming E-mails sent to both servers by the mail daemon so I have two copies? Or is my only option having the primary mail server forward the E-mail somehow to the old mailserver ?
Best Answer
After the new mail server is ready to accept mail for your domain via smtp and serve mail via imap and or pop or the like, then you want to change the old server to forward mail to the new server. Get all this working BEFORE you change MX records. Then it doesn't matter if mail arrives at either the old or new server, since it all ends up at the new server, eventually.
I dislike people using the term "propagation" when referring to most DNS changes, as I find that most people are being mislead to what is going on. Typically DNS changes are instantaneous, there is no need for propagation. Propagation only happens when you are changing the nameservers at the registrar, and these changes need to go out to all the root DNS servers. This is an operation that used to take many hours in the (distant by internet standards) past, but no longer takes much time. These days when people talk about propagation, they are usually incorrectly referring to DNS TTLs.
Whenever an authoritative nameserver answers a DNS question (like what are the mx records for this domain), that answer comes with a TTL, which says "here is your answer. You can assume this answer is the correct answer for X seconds". So if you have a very long TTL on your MX records, and then change them. People that looked up your MX records might cache the results for a long time, and therefore, after the change, will be sending mail to the wrong server for a long time. If you are anticipating a change in DNS records. You can drop the TTL to something small until after the change.