How do I stop Outlook trying to send non-existent messages?

[Ingenue]

After by mistake double-clicking the message send button on a message with an
attachment, every time I use send/receive Outlook tries to send one or more
non-existent messages. The dialogue box remains open until it receives a
message that the server has timed out. Real messages are meanwhile received
and sent properly.

At the same time, messages are no longer sent directly when the "send"
button is pressed, but sit in the outbox until "send/receive" is used.

 

[Roady [MVP]]

Could these be read receipts?
See http://www.howto-outlook.com/howto/deletereadreceipt.htm

As for the Send/Receive issue; are you sure Outlook is in on-line mode?
Verify that File-> Work Offline is unchecked.

 

[Ingenue]

Thank you; seems to have worked. How do I stop it happening again, do you
know, please?

 

[Roady [MVP]]

Set Outlook to prompt you before sending a receipt (this is the default);
Tools-> Options-> Email Options-> Tracking Options