Sending mail with "sent" is fast, but copying the sent mail is very slow, sometimes takes a minute; can it be speeded up?

After hitting "send", a screen comes up showing a moving bar "copying the mail to the sent folder", the bar goes fully right on the screen but then I must wait, sometimes a minute for the copying process to complete. Then I always get a screen message next that says in effect could not copy, so I close that screen and then go to my sent folder and the email I sent shows up. So, the copy process is very slow and then I get a message could not copy, but in fact a copy does appear in sent folder????

Thank you