SMTP Timeouts

 Over the past couple of weeks I have been receiving SMTP server timeouts at times when attempting to send out an e-mail. I use Mozilla Thunderbird as my e-mail client. The timeout message pops up immediately after I click the "Send" button. If I click "Send" again, it usually then goes through. Sometimes I have to try a third time. I can understand this message coming up after a few seconds of attempting to send an e-mail, but not immediately. This does not happen each time I try to send an e-mail but happens randomly. Has anyone else experienced this issue?

JohnD