Using MAPI to send EMails to outlook question

I have found out why i could send Emails via my program on some machines and
not others.
The users that had there messages set up to use HTML in their signatures
were not getting the Emails sent to outlook.
Is it possible to add some code so that even HTML signatures will be
included when send Emails via MAPI ?
If it is possible then any help would be great.

Many thanks
John