Created attachment 8492643 [details] kzembower_Thunderbird_Troubleshooting_Info User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:32.0) Gecko/20100101 Firefox/32.0 Build ID: 20140830210550 Steps to reproduce: I'm trying to send an email greater than 2000 characters. Actual results: I tried to send an email greater than 2,000 characters. The pop-up window showed 'connecting to smtp...', 'connected to smtp...', . It often then shows 'Delivering mail' with the crawling slug. Sometimes it shows '92% completed'. Other times it shows '100% completed'. Regardless, after about 30-60 seconds, The pop-up says "Sending of message failed. The message could not be sent because the connection to SMTP server smtp.verizon.net timed out. Try again or contact your network administrator." I used 'Save as...' to dump the largest email I could send to myself as an .eml file and counted the characters. The largest was 1895 characters, including all headers; everything in the .eml file. I believe that the limit that prevented sending was less than 100 characters above this. This is a recent development. As recently as two weeks ago, I could send long emails without a problem. I was not notified by my ISP, verizon.net, of any changes. I am a Ubuntu user, and apply all patches as soon as they are made available by Ubuntu. I've recently updated my system, but am not certain Thunderbird updated at this time. I've attached the Troubleshooting information from Thunderbird. Expected results: Message should have been sent.
Did you changed something in your network ? This sound like an MTU issue...
Note that I do have a transcript of a manual SMTP session, using telnet and openSSL, in which I was successful in sending a short, test email to myself. In the transcript, you can see the parameters for data enchange. Let me know if this is of interest and I'll post it. Thanks for your help and interest in solving this problem. -Kevin
I do not know if you get a packet that exceeds the size of your mtu if you do it with telnet/opensssl. My comment meant: Please check if you have a mtu issue on the network level and/or if the mtu path discovery is working (for ipv6).
Thank you for your thoughts and suggestions. No, I was not trying to test the MTU with the telnet/openSSL test. I was trying to display the SMTP parameters, and check if SSL Auth was working correctly. I don't know how to check for an MTU issue. I do not use IPv6. I think that Thunderbird should work correctly regardless of the MTU setting. I don't believe that MTU is a parameter that is settable from within Thunderbird.
The MTU is something basic on the networking connection and the parameter is not settable from within Thunderbird. You can or better should ask in the Ubuntu help Forums if you don't know how to check your MTU settings.
sounds like a network config issue.