I want certificates that affects each domain on my small server. Individuals domain names share exactly the same ip but have different domains (hosting that is shared) I am wondering will i require a specific certificate for all of them or can one purchase one certificate that is applicable for them all? The main reason I want certificate happens because the organization which our server relays our clients mail to has blocked smtp port 25 so we have to use ssl port.

We're using Parallels Plesk btw.

You cannot generally host several SSL domain on one ip, unless of course you will get away with utilizing a wildcard certificate (i.e. certificates for *.example.com) or unless of course you are able to depend on all of the people being able to access your website getting a browser with SNI enabled.

However miss out on in what manner the SSL certificate you utilize for you personally website hosting is definitely an anyway highly relevant to using smtp over ssl. You do not need certificates for your (unless of course your smtp host mandates using client side certificates, but that appears somewhat unlikely).