A Mail that I tried to send (unsuccessfully) now keeps flashing up for a second and repeats over and over
I have macOS Mojave. A while ago I tried to send a mail message but that was not successful. This message now keeps on flashing onto the screen. I have tried other suggested remedies going through Finder / Library / Mail. Two items are listed there "Persisenceinfo.plist" - which has one item (unrelated) in it dated two months before this flashing occurrence and "V6" (no V3) - which has 5 items in it, four of which are a string of letters and number and a 5th one "MailData" which in turn has several items but none of them relate to the mail that is flashing.
The flashing mail interrupts one when one is typing on any other application - this is most irritating.
Would be most grateful for help to get rid of this bothersome feature!