Our SMTP aims to maintain a high sending reputation to prevent it from being compromised we use we have more controls on the smtp sending flow, one of which blocks the "sender" if it sends more than 300 emails to addresses in an hour that are invalid, the system in this case believes that you are sending email without knowing the recipients.
When the block intervenes in the control panel, the following message may be displayed:
Domain xxxxxxxxxx.smtp.utixo.net has exceeded the max defers and failures per hour (300/300 (80%)) allowed. Message discarded.
The messages are rejected, this to avoid that the antispam systems lower the reputation of the IP if they detect this condition, our system intervenes before the target systems do.
This block is then automatically removed after one hour.
The SMTP service is not designed for low quality email marketing campaigns that contain a high number of "bounces" and prevents this from being done, for mailing marketing Utixo has another specific Pulse Mailier service.