Sent  Mail not showing up in Sent Folder

[bladerunner88]

So recently sent mail is not showing up as sent in my sent folder am using a MBP OS X 10.10.5 Mail Vs 8.2.
I know recipients are receiving it as they respond, but it would be good to have the confirmation sitting in my sent folder. this seem to be happening if my e-mail contains pictures and size can be between 2.5-3.5 Mbs.
Anyone have any thoughts or settings I could tweak?

TIA

 

[hxlover904]

In Mail, Preferences, Accounts, Account information- do you have send large attachments with Mail Drop checked?

Are the messages getting deleted from another device? Do they show up in the sent folder on other devices?

That's the only thing I can think of.