Why is Thunderbird showing a 'rejected' error when sending outgoing mail?

[cepheid]

For those who use the Thunderbird mail client, I'm wondering why this message pops up every time I try to send an outgoing message. I'm accessing my university e-mail accounts by accessing their servers as IMAP servers. Here is the error message I get after clicking 'send.'

An error occurred while sending mail. The mail server responded: 5.7.1 Rejected 24.86.226.249 found in dnsbl.sorbs.net. Please verify that your email address is correct in your Mail preferences and try again. ​

Any help with this would be appreciated.

 

[z-component]

Well have you ever successfully sent mail on your school's server or is this a new error? If not, I'd say it's probably your security settings. You should try to search your university's website for explicit instructions for setting up Thunderbird or another mail client so you can mimic the settings.

 

[cepheid]

It's a new error. I alreday set up Thunderbird the first time around using explicit instructions on the university website. That having been said, I'll look into it.