Why an email bounced, and domains Solstral pauses for you

When an email doesn't arrive, the server that refused it says why. Solstral reads that answer and puts it in plain words on the campaign report, next to the server's own text.

The reasons

• Mailbox full: a temporary problem. The address stays on your list.
• No such mailbox or Domain can't receive mail: the address is dead and goes on Do not email.
• Blocked by the receiver's policy or Rejected as spam: the receiver objected to the sender, not to the person. The address stays on your list; it moves to Do not email only if it keeps failing for two weeks, like any temporary failure.
• Greylisted: the receiver asked us to try again later, which happens automatically.
• Receiver is limiting our rate: see below.

Domains paused for you

The big email services judge a sender by how it behaves towards them, so Solstral pauses mail to a single receiving domain when that domain pushes back:

• Microsoft blocks your mail (Outlook, Hotmail or a company on Microsoft 365): campaigns and flow emails to that domain wait 24 hours, because sending on into a block makes it last longer. Your admins are told.
• A receiver says you're sending too fast (Gmail's "unusual rate" message, for example): mail to that domain waits 15 minutes, then 30, up to 4 hours if it keeps happening. Everything else carries on at full speed.

Only campaigns and flow marketing wait. An email a person sends from a record always goes. Waiting emails are sent when the pause ends; nothing is dropped. The Receiving domains card on the Marketing page shows what's paused, what the receiver said, and the domains whose emails failed most and why. An admin can press Send again now to end a pause early.

If Microsoft keeps blocking you

The block is usually about the sending IP address or your domain's recent complaint rate. Check your list hygiene (old, unengaged addresses), then ask Microsoft to review the block through its sender support form, quoting the code in the message (for example S3150).