but why ?
if she/he need to just do it asynchronously, why she/he need 3rd party
component?
The thread with event rised when the mail couldn't be send is a quite
good solution. But rather for WinForm. In the web the solution I know
is to put mail's in some queue (for example database or flat files with
mails). And use external service (windows service) to handle mail
sending.
If your web application will grow, then a lot of mails will be
generated, and only dedicated service would be able to handle it.