A detailed description of Bouncing can be seen here.
Dealing with a subscriber whose email is bouncing
The linked description above explains what 'bouncing' is. However, what can owner/mods do to help the subscriber deal with the situation?
First, realize that groups.io can't fix it*. The subscriber's email service provider is blocking delivery of emails from groups.io to the subscriber. Until that block is removed by the service provider, no messages will get through to the subscriber, including bounce probes.
To resolve bounces:
- Go to subscriber's page (Admin->Members) and view the email delivery history bounce error messages ("Recent Bounces").
- Please also note that 400-level errors usually indicate a temporary condition, such that the message in question could subsequently be delivered.
- 500-level errors are considered permanent.
- There are several good resources on the web to help you sort out SMTP error codes -- here and here.
- Communicate those errors to tech support at the subscriber's email service provider AS THEY ARE THE ONES DOING THE BLOCKING.
- Generally the subscriber will have to do this.
- Wait til tech support at the subscriber's email service provider says they have fixed their problem or whatever they are doing to block the email from groups.io.
- Now send a bounce probe to see if the problem is really fixed. See this message on how to send a bounce probe.
- If the bounce probe email is delivered and the subscriber responds to the probe (clicks on the link in the email), groups.io will resume sending email to the subscriber.
*Note - Sometimes an email provider will have groups.io listed on a "spam black list". Mark at groups.io may have to get in touch with the black list host and/or the email provider to straighten out the problem.
Unfortunately, there are many dimensions and aspects of this problem and there is no "magic wand" to vanquish the beast when it raises its ugly head.