How can I know if error happens when sending mail?

[Chengqi(Lars) Song]

Hi,

I'm using msmtp to send mail. I've set sendmail_wait=-1 in .muttrc to make 
sending mail not blocking. But there comes a problem. If any error happens when 
sending mail, I will not aware about it. And sometimes it cause trouble to my 
work. How can I solve this problem? I need to be told if error happens in 
sending mail. 

Thanks
Lars