"send/receive complete" appears while dial-up is still sending.

[John Ruhl]

When I'm sending a large file from Outlook via dial-up connection, the
"sending 1 of 1" (as I recall) indicator is replaced by "send/receive
complete" almost immediately while the modem continues to send the document.
The only way to know when it's done is to monitor the connection indicator to
see when the "bytes sent" stops increasing. This is a recent phenomenon; The
"sending 1 of 1" indicator used to stay on until the transfer was complete.

 

[Russ Valentine [MVP-Outlook]]

Not surprising. Current versions of Outlook were not developed nor optimized
for dial up connections. I know of no development nor troubleshooting
information in this area.