Sending email on behalf of user via SMTP?
<p>I'm building an app to allow my users to send email.  I want the email to originate from their domain.   Currently, email is sent on behalf of my Mandrill account with their name/email used for the From header.  It "works" but most of the mail is not delivering as best as I think it could.  </p>

<p>The way I see it, one option is to use a service like Mandrill, Mailgun, Sendgrid, etc and have my users update there TXT records to verify their domains, thus allowing me to send on behalf of my users.  Is that correct?</p>

<p>I'm wondering if another option would be to collect SMTP credentials, and then send the message via SMTP for my user, thereby preventing my user from having to log in and update their TXT records before using my app to send messages.  I think it would be far easier to simply add SMTP credentials.  Is this possible?</p>