DNS MX record change

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wolfrR1der
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Joined: 2020/04/13 17:42:58

DNS MX record change

Post by wolfrR1der » 2021/06/21 16:46:47

This is probably easy for some of you but I can't seem to find the answer. We are moving our email to Exchange Online soon and while they do provide the DNS entry we need to change to I can't figure out exactly how to change it. Our current BIND9 entries are:

; Mail Exchangers
MX 10 mail ; Primary Mail Server
MX 50 mail2 ; Secondary Mail Server

The record Microsoft provides is: blah-blah.mail.protection.outlook.com

My knee jerk reaction is to just change to the following:

; Mail Exchangers
MX 10 blah-blah.mail.protection.outlook.com ; Primary Mail Server

Would that be accurate or should this be a CNAME instead?

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TrevorH
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Re: DNS MX record change

Post by TrevorH » 2021/06/21 16:50:30

You want an MX record. And you probably want two of them, with different weights, both pointing to different MS servers which they presumably tell you. You may also want TXT records set up for SPF and maybe also stuff to do with DMARC.
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wolfrR1der
Posts: 18
Joined: 2020/04/13 17:42:58

Re: DNS MX record change

Post by wolfrR1der » 2021/06/21 16:52:52

We have working SPF records. Changing it to the MS provided one is straight forward.

Is the way I want to change the MX record accurate? If it is I will dig up a second record from them to have two if at all possible.

Edit: In thinking about it I am guessing I am missing a trailing "." so that DNS doesn't attempt to append 'company.com' to the address correct? So it should be:

MX 10 blah-blah.mail.protection.outlook.com. ; Primary Mail Server

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TrevorH
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Re: DNS MX record change

Post by TrevorH » 2021/06/21 16:55:30

Well I can show you (obscured) ours but they point to mimecast before the mail goes off to O365:

Code: Select all

$ dig MX company.com
...
;; ANSWER SECTION:
company.com.		3600	IN	MX	10 eu-smtp-inbound-2.mimecast.com.
company.com.		3600	IN	MX	10 eu-smtp-inbound-1.mimecast.com.
...
CentOS 6 died in November 2020 - migrate to a new version!
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 is dead, do not use it.
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wolfrR1der
Posts: 18
Joined: 2020/04/13 17:42:58

Re: DNS MX record change

Post by wolfrR1der » 2021/06/21 17:39:00

Thanks. I gather from that info that my second posting was correct. I need the trailing "." or it will append our DNS suffix to it.

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