Error logs and & valid server


I have a new campaign that looks bad in terms of open rate, when I'm checking the application log it seems like something is not work:

2020/10/12 16:58:02 [error] [application] Cannot find a valid server to send the campaign email, aborting until a delivery server is available!Campaign UID: mc1553cv1ff51
And here you can see the status (I just paused it):
What could be the issue? Delivery servers seem work, and it sending - Anything I can do to understand better the error here?


I checked, and this is the only case that could be relevant to me, I'm asking if it's an issue to use the same setting for 2 different delivery servers?


Active Member
Staff member Support Staff
Fatal error
- a fatal error means a SMTP error that has a return code higher or equal to 450.
- this happens when for example the account we try to send the email does not exist on the target server, or it has been closed.

Soft error
- a soft error means a SMTP error that has a return code lower than 450 but higher than 2xx(which is a success code).
- this might happen if the subscriber account is temporarly disabled, or the receiving server is too busy, etc. Usually you'll want this option set to a high number.

Hard bounce
- after the email has been delivered, there are chances the target server will bounce it back for several reasons.
- a hard bounce means the email does not exist anymore on the target server, or it has been blacklisted, disabled, etc.

Soft bounce
Unlike hard bounces, soft bounces can happen for reasons like server/account temporarily unavailable, not enough disk space to store the email on the server, or even the response of an autoresponder.