Recipients modified email messages (using event sink) sent from PICKUP folder and lands in the DROP folder ?
The Pickup folder processes outgoing messages that are created as text files and then copied to the Pickup folder. When Request for Comments (RFC) 822 messages that are correctly formatted are copied to the Pickup folder, the SMTP service initiates delivery. In this replay method, the X-Sender envelope field and the X-Receiver envelope field are written to the e-mail message when the SMTP service puts the e-mail message into the Drop folder.
Note The SMTP service puts the e-mail message into the Drop folder for local delivery on a computer where Exchange is not installed.
In this scenario, the Pickup operation honors the envelope fields that are written to the e-mail message
This is because, we will have an default domain entry in the SMTP mail area of IIS. This is the process that handles all mail that comes into your SMTP system that is not otherwise specified. This mail would be delivered based on the settings you make in the properties area of that default setting. This includes the name of the server that the mail claims to be from.
In addition to this default entry, you can also create an Alias Domain for any other domains you might own. Each one can have its own name. So where your default might say mail is coming from Mydomain.com, you can set up alias domains for domain.com and minedomain.com. Once you have those aliases set up, each alias then sends its mail to the DROP folder associated with that alias. The mail will sit there in the DROP folder, waiting for further processing. It assumes that another system is going to poll that DROP folder and do something with the mail.
If you end up with mail messages in your DROP folder because you created an alias domain by accident, simply delete that alias and then stop and restart the mail server. Now drag all the messages from the DROP area back into the PICKUP area. They will process through the default queue, following your normal rules and get out to your recipients.