Mail 8.2 Connection problems with SSL Email

Mail 8.2 running on Yosemite will not connect to my email client 123 reg since they have now insisted on using port 993 and port 465 for SSL on both. I’ve been told Mail 8.2 is too old for modern requirements? Is there anyway I can use a work around to continue to use Mail 8.2? (I can’t update as I have design software on my iMac which won’t work if I update)