Outgoing Email Won't Work

[HRJR]

Recently, I deleted an old email from Mac Mail. Since then outgoing emails won't send. I'm guess for a long time, my outgoing emails were using the server from the older email. I contacted my email host company and we tried numerous combinations of settings for the smtp server, none of which worked. Incoming mail works fine and incoming and outgoing work fine on my iphone. Is it logical to try using the server settings on my iphone in Mac Mail or is that a different animal? I verified and repaired permissions but afraid to go any further into the library settings (which is what someone was suggesting). I'm using an older iMac with OS 10.10.5 Yosemite. I haven't upgraded my OS because I don't want to lose functionality with several programs that work just fine now. Since the email was working fine for years before I deleted that old email, I think it's safe to assume the issue is related. Just not sure how to fix it. Thanks for any help. BTW, if I try to send an email, I get the standard error window about can't sent / connect with server. There's only one server showing smtp.myemail.com