Exchange 2016 Environment DNS entries help

Mr. Jones

I'm trying to troubleshoot my exchange environment not being able to receive inbound emails. Emails work within the domain, and they send out, we just can't receive outside communications. We host with GoDaddy so there's DNS entries there to worry about, but they haven't been touched, so let's assume they are good. lol

Using nslookup -querytype=mx mydomain.com returns:

Server: PDC.mydomain.com
Address: <PDC IPv4 address>

mydomain.com MX preference = 10, mail exchanger = mail.mydomain.com

So I feel like my MX is at least functional, but I'm not great with DNS yet.

Furthermore, using nslookup -querytype=a mail.mydomain.com returns:

Server: PDC.mydomain.com
Address: PDC IPv4 address

Name: EXCHSERV.mydomain.com
Address: <EXCHANGESERVER IPv4 Address>
Aliases: mail.mydomain.com

I have a feeling I'm missing a DNS entry. My DNS entries are as follows:

CNAME=autodiscover - mail.mydomain.com
CNAME=mail - EXCHSERV.mydomain.com
A=EXCHSERV - EXCHSERV IPv4 Address
MX=(same as parent folder) - [10] mail.mydomain.com

Anything stick out to you guys? What would be your next move?

EDIT: nuked a server earlier and am picking up the pieces. I think there was only ever one IP exemption for SMTP 25 and it was the server I nuked (running dual exchange environment). I'll have to wait until tomorrow to do anything with the firewall as I don't have the password memorized and I'm working from home atm. Will update with resolution when I sort it out.

EDIT #2: Issue is resolved. The firewall was set to allow traffic to only the server I nuked.

syko24

@Mr-Jones - check your firewall and make sure port 25 is forwarding to your Exchange server.

Try https://canyouseeme.org/ and check port 25

nadnerB

Also, have a look at https://mxtoolbox.com/
That has a heap of tools for troubleshooting, and will check your external DNS records too.

Mr. Jones

@syko24 That's not going to help me atm, as I'm tunneled in, but it's a good resource and I appreciate that.

Mr. Jones

@nadnerB yea. I've been using that, but I'm guessing I need to sign up for something, because it's not telling me much. Definitely less descriptive that nslookup unless I just don't know how to use it which is a great possibility.

syko24

@Mr-Jones - on mxtoolbox just type in the search line:

tcp:mail.mydomain.com:25

Press enter and see if it says the port is open.

Mr. Jones

check your firewall and make sure port 25 is forwarding to your Exchange server.

Going to look into that for sure. Thank you!

Mr. Jones

@syko24 said in Exchange 2016 Environment DNS entries help:

@Mr-Jones - on mxtoolbox just type in the search line:

tcp:mail.mydomain.com:25

Press enter and see if it says the port is open.

Thanks. It throws an "unable to connect" and then lists the GoDaddy IPv4 address that's associated with the A record of mail.mydoamin.com

syko24

@Mr-Jones said in Exchange 2016 Environment DNS entries help:

@syko24 said in Exchange 2016 Environment DNS entries help:

@Mr-Jones - on mxtoolbox just type in the search line:

tcp:mail.mydomain.com:25

Press enter and see if it says the port is open.

Thanks. It throws an "unable to connect" and then lists the GoDaddy IPv4 address that's associated with the A record of mail.mydoamin.com

So either a firewall issue or your isp may be blocking port 25. Is this business internet with a static ip?

Mr. Jones

So either a firewall issue or your isp may be blocking port 25. Is this business internet with a static ip?

Yes. Time to look at the Firewall.

dave247

@Mr-Jones said in Exchange 2016 Environment DNS entries help:

So either a firewall issue or your isp may be blocking port 25. Is this business internet with a static ip?

Yes. Time to look at the Firewall.

and check your NAT settings ^^