When an email address is not valid, Symphonie marks the email address as bad by putting the recipient "on hold."
Recipients that are held are not sent any further emails to preserve your Reputation Score with the Internet Service Providers (ISPs).
The ISPs keep a metric of how many attempts are made to send to invalid email addresses, and a high rate will result in your email
being sent to the bulk folder, or even having your sending blocked.
Symphonie can detect invalid email addresses in a variety of ways. All imports are checked for the correct physical layout of the
email address, looking at factors like whether the email address contains one (and only one) @ sign, is composed of the allowed characters, etc.
After this every domain is looked up in DNS to verify that an entry exists that provides the location where email should be sent (has
a MX record). Finally, when sending an email if the delivery fails, Symphonie looks at the textual message from the mail server
and attempts to parse out if the message indicates the email address is not valid. Messages that are about other factors, such as
a full mailbox or the message being classified as spam, do not cause Symphonie to mark the email address on hold.
Held recipients are immediately removed from any subsequent emails sent by Symphonie. You do not need to do anything to make sure
that held recipients are excluded from your sendings - Symphonie does this for you automatically, every time.
These API functions allow you to determine if an email address has been held, to mark new recipients as being on hold, or to remove
a recipient from being held. Do not use the held mechanism to control list distribution. If you want to exclude recipients from
receiving your emails, add them to a suppression list rather than marking them on hold.
We recommend that you be very cautious about removing a recipient from on hold. If the email address was invalid before, it is
rarely suddenly valid, and so your Reputation score is likely to suffer from having a high unknown user rate.