@mucksiegooma
Welcome.
I'm not saying that I can assist, but I know my forum colleagues are in a similar position until you part with a touch more information.
Which Mac (year, model, OS, at least)? When was Mail last working normally? Any updates or upgrades since then? Any new apps added?
Have you tried the basic response to malfunction; like repair permissions, rebooting your Mac?
Do you have any backups like Time Machine, a cloning BU?
I know these questions are tiresome, but only you know what Mac and OS you have; only you know what you were doing and what steps you have already taken to remedy the problem.
Bear with us, we are here to help.
Ian