Exchange 2016 and SMTP problems where is fotigate and fortimail

[drClays]

Hello,

I have a problem with SMTP on Thunderbird and it's probably the wrong configuration on fortigate or fortimail.

This is my configuration:

External DNS:

mx set on mail[.]domain[.]com
1.2.3.4 "A" mail[.]domain[.]com
1.2.3.4 "A" owa[.]domain[.]com
1.2.3.4 "A" autodiscover[.]domain[.]com

Internal DNS:
mail[.]domain[.]com - 10.0.0.150 - FortiMail
owa[.]domain[.]com - 10.0.0.120 - Exchange Server
autodiscover[.]domain[.]com - 10.0.0.120 - Exchange Server

FortiGate Firewall Policy:
1.2.3.4 [port 25] -> 10.0.0.150 [port 25]
1.2.3.4 [port 465] -> 10.0.0.150 [port 465]
1.2.3.4 [port 993] -> 10.0.0.120 [port 993]
1.2.3.4 [port 995] -> 10.0.0.120 [port 995]
1.2.3.4 [port 443] -> 10.0.0.120 [port 443]

That's what I saw:

Internal network:
When I configure IMAP settings on Outlook and I set servers on owa.domain.com then I can receive emails and send emails.
When I configure IMAP settings on Thunderbird and I set servers on owa.domain.com then I can receive emails but I can't send emails.
When I configure IMAP settings on Thunderbirds and I set servers on mail.domain.com then I can receive emails and send emails.

External network:
When I configure IMAP settings on Outlook and I set servers on owa.domain.com then I can receive emails and send emails.
When I configure IMAP settings on Thunderbird and I set servers on owa.domain.com then I can receive emails and send emails.

In exchange Send Connector is set up on 10.0.0.150 - FortiMail

FortMail Settings:

Why on Thunderbrid(in the internal network) server settings don't work on owa[.]domain[.]com?

[Anonymous]

Hello drClays, 

Thank you for using the Community Forum. I will seek to get you an answer or help. We will reply to this thread with an update as soon as possible. 

Thanks, 

Raja- Fortinet Community Team 

[Markus_M]

Hello DrClays,

you will need to define more what "cannot send mails" means. Does thunderbird SMTP connect to the server?

If so, what does it speak and do you have logs from the exchange server with this connection?

If not, prior an SMTP connection one would assume a DNS resolve attempt for the MX record and following for the A record to get the IP of the server to connect to.

Which of these fails?

Best regards,

Markus

[drClays]

Hi @Markus_M,

thanks for the reply.

This configuration works 2 days, after that, I see again error where Thunderbird cannot connect to SMTP server:

In the exchange connection logs, I do not see anything indicating that there is a connection to Thunderbird.

I tried to change in local DNS A record from local IP to external IP, but this is making problems with internal applications that use owa.domain.com server