For the last week or so I have been unable to send attachments using thunderbird. Mails with no attachments work just fine. Have tried different smtp-accounts with no luck and even downloaded a different mail client and this also works fine. Someone else had this problem, (https://support.mozilla.org/en-US/questions/1021852) he wrote "progress bar that will read a 80 to 95 percent completion and then stay there till it times out after a few minutes. I get this error: Sending of message failed. The message could not be sent because the connection to SMTP server outgoing.verizon.net timed out. Try again or contact your network administrator. " It is the same with me, only he went over and checked his smtp settings and then he was fine. I have had no such luck.