Summary of SmartRelay constraints
You should consider the following constraints when setting up and using SmartRelay:
SmartRelay imposes a one recipient per message limitation for injected messages
A message can be sent to only one RCPT TO address. Note that To:, Cc: and Bcc: headers are not applicable to SMTP.
See Supported email messages for more details.
SmartRelay imposes a limit on the number of simultaneous SMTP connections between your local SMTP forwarder and your dedicated SMTP listener
See Maximum number of simultaneous SMTP sessions for more details.
By default, we apply an inbound rate limit of approximately one message each second, around 100,000 messages each day
See Inbound rate limiting at the SMTP listener for more details.
If you enable the creation of new deliveries option during setup, new deliveries are sent as TRANSACTIONAL or NEWSLETTER, according to the default that is set during configuration.
It is important that you always specify whether the delivery should be TRANSACTIONAL or NEWSLETTER (a bulk or marketing delivery), as this affects suppression list management.
If link tracking is enabled, it is applied to all links in your emails
See SMS Message Requirements for more about SMS message constraints