Using Gmail SMTP to send email in Gnus

[Azhaguselvan]

Hi,

I have two gmail accounts A and B. I forward B account's email to A's
gmail inbox and
fetch those mails to my local dovecot server using offlineimap and
read it using gnus.
Now how do I configure, the smtp server for gmail so that I can send
mail through both
the email addresses dependent on from which the mail is received??

I searched the forums, most of the solutions are based on deciding the
id based on
the From: field. But, cos I gather the B's mail to A's inbox and then
download, the
From: field is always setup as A only.

Please suggest.