I posted a Question about Thunderbird but it was posted under All Products. Can I move it to the Thunderbird Forum?
Using Microsoft smtp.office365.com Server, Send fails to all accounts at Comcast.net Using Thunderbird, When I send to someone@comcast.net, I get an error back after about 24 hours. Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond. If I send a message using a Web based service or using my Cell Phone, there is no problem with Comcast. Info from my Sys Admin: 2 messages that you sent that are listed as “Pending”. Here is the information on the reason: Reason: [{LED=421 4.2.0 service unavailable};{MSG=}
Using Microsoft smtp.office365.com Server, Send fails to all accounts at Comcast.net
Using Thunderbird, When I send to someone@comcast.net, I get an error back after about 24 hours. Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond. If I send a message using a Web based service or using my Cell Phone, there is no problem with Comcast. Info from my Sys Admin: 2 messages that you sent that are listed as “Pending”. Here is the information on the reason: Reason: [{LED=421 4.2.0 service unavailable};{MSG=}
Opaite Mbohovái (1)
looks to be in Thunderbird to me, so I will close this as a duplicate of https://support.mozilla.org/en-US/questions/1205987