Outbox message repeatedly sent, not going to Sent folder

Might eM Client SMTP software have a limiting time (max number of seconds) allowed for an Outbox file to be completely moved to server, before possibly cutting to stop, if not completely sent?. Then to later retry again?
I recently had a file basically containing a website address for distribution to 30 recipients. (No pictures, so considered a small file.) Some replied advising received message 22 times in a day, while file still remained in Outbox folder. Not appreciated! It never moved to Sent folder. Eventually deleted Outbox file to stop more transmissions. Any explanation??
My server connection is wireless, and consider it low grade speed. The server provider advised transmissions on this messaging averaged 31 seconds.
For my “Menu-Settings-Sent”, all three options activated. The “Send Later” is not activated.

I am “lmurdoch” = Leigh Murdoch. I am a first time user of this service. Hope some understanding of my situation can be clarified for me. One suggestion from my server provider, that might be helpful, is to reduce the number of recipients sent a message to say 10 to 15 persons. But suspect there is more to it than that.