I have been using desktop version for about a year with the plan to upgrade but recently I have started having problems

Unfortunately emails will no longer send and sit in the general outbox. I thought at first in might be the email server but it was not and I have tried everything i can think of apart from uninstalling and re installing the software. I am currently running desktop 7.2.2

I know my server is working because I have had to load another email client to continue working. And incoming mail is working fine.