Answer:
When you compose and send an Agent Response or Agent Email in iService, the system generates the message and relays it to the SMTP server that is defined for the mailbox you used. The mailbox used will normally be same as the mailbox that received the message, unless you pick a different mailbox when sending the message. Once the mail server accepts the message iService has no knowledge of the path that message takes on the way to the recipient. If the message is returned by the recipient's mail server as undeliverable, you will see an undeliverable message in your queue and the customer's email address will be marked as isBounced. There are various reasons why the customer's mail server will reject an incoming message (mailbox full, considered SPAM, etc.), which are beyond the scope of this article.

There are a few places you can check within the iService interface, other than the _undeliverable topic, to troubleshoot.

1. SMTPOut Tab - When you send a message, iService populates a table of messages to send named SMTPOUT. Normally they are passed to the designated SMTP server within a few seconds, but if iService is unable to relay the message for some reason you will see it listed in the Admin Tools - SMTPOut tab.

2. Mailbox Tab - When a message fails delivery, an error might be returned from the mail server with details. These errors are listed at the bottom of the Admin Tools - Segment - Mailboxes tab.

In most cases, if the recipient's mail server rejects your message for SPAM purposes it will not send a bounce message.

NOTE: For a small fee, our technical services team can review internal mail server logs and determine exactly how a message was handled. You will need to provide the email address of the recipient and the time the message was sent. To request this service, contact us using support@1to1service.com.