Trouble with SMTP traffic

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1

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Expected Behaviour:

I expect SMTP/mail traffic to work, but it doesn't. I have 3 e-mail accounts configured on my iPhone (Office365 hosted Exchange, 1 Yahoo personal, 1 Gmail personal).

Actual Behaviour:

The connection just keeps trying, but never connecting. No send or receive when using PiHole as DNS. The Outlook application on my PC also does not work, it won't even connect to the server.

The blocked site log doesn't show anything as being actively blocked, so I'm not understanding why my mail applications aren't working correctly.

I'm using my firewall (pfSense) as my DHCP server, it is using OpenDNS for its DNS queries. If I remove the setting to force piHole as the DNS server on the LAN, everything works fine. Also, web browsing works fine w/ piHole as DNS, it's just the e-mail apps won't work properly.

What am I doing wrong, or how can I troubleshoot? Would packet captures be of any use? Anyone run into this before? I didn't see anything posted in this forum describing a similar situation.

2

I don't know if it is a similar situation, probably not, but to add this to the topic...

I have my router as DHCP server and I don't have pfsense.
After some playing with pihole setups, I got in the situation that I can't send
smtp mails. First I was trying to find my own mistake.
After some days the problem has dissapeared. I don't know if this was a setup
problem. Weeks later I found myself again in the same situation and thought,
maybe by various testings and router reboots, the provider has blocked my account.
I called them and he brought me to the idea, to change the router settings:
In my router I have a secure list of email servers.
I disabled this security feature, and the problem has immediately gone.
Finally I don't know, what the problem really was, I never changed my email account.
I am staying with this setup and did'nt try if I maybe can go back to the secure list.

Edit: DHCP Server