Thunderbird triggering ISP spam filter on send
Hi, I've used Thunderbird on Linux for about 20 years and it has worked flawlessly connecting to my ISP mail for both sending and receiving messages. About 2 weeks ago I tried to send a mail and got an internal error back from the ISP SMTP server that the message was being blocked as possible spam. POP continued to work fine.
I tried renaming my local .thunderbird directory and downloading the latest version of Thunderbird to try a fresh install. It behaved exactly the same way.
The frustrating thing is that KMail, an alternate Linux mailer works fine with the exact settings that fail on Thunderbird. I can also send mail from my phone when connected to the same ISP wifi as the Linux machine.
I am not sending out messages to large groups of recipients. It will fail (but work in Kmail and K9Mail on Android) with a trivial test message to myself.
Any ideas how I can troubleshoot this? I like Thunderbird but can't use it if I can never send mail.
Thanks!
Modified by Matt
Chosen solution
- Sigh* I think I finally solved the problem. My ISP router assigns DHCP addresses to internal machines as expected but tends to keep the same IP for every MAC address between connections. Telling it to assign a different internal fixed IP to my internal machine and then restarting the wireless interface somehow bypassed whatever spam block the ISP put on their SMTP server.
In short: 192.168.0.4 internal address -> fixed WAN external address -> SMTP = error, spam detected. Set the DHCP to assign 192.168.0.6 to the machine it used to "randomly" give 192.168.0.4 all the time. 192.168.0.6 -> fixed WAN external address -> SMTP = mail sent correctly.
I have never looked into the minute details of DHCP addressing so I did not consider that and wasted a lot of time because I didn't know *why* the ISP flagged the email as spam.
Thanks to sfhowes for your suggestion.
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Do your accounts in TB have signatures? I think you have to find out from the ISP how they classify spam.
Chosen Solution
- Sigh* I think I finally solved the problem. My ISP router assigns DHCP addresses to internal machines as expected but tends to keep the same IP for every MAC address between connections. Telling it to assign a different internal fixed IP to my internal machine and then restarting the wireless interface somehow bypassed whatever spam block the ISP put on their SMTP server.
In short: 192.168.0.4 internal address -> fixed WAN external address -> SMTP = error, spam detected. Set the DHCP to assign 192.168.0.6 to the machine it used to "randomly" give 192.168.0.4 all the time. 192.168.0.6 -> fixed WAN external address -> SMTP = mail sent correctly.
I have never looked into the minute details of DHCP addressing so I did not consider that and wasted a lot of time because I didn't know *why* the ISP flagged the email as spam.
Thanks to sfhowes for your suggestion.
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