See also the official documentation in:

• Help Center > Group Owners Manual > Managing members > Checking for bouncing members
• Help Center > Group Owners Manual > Additional information > Groups.io bounce handling
  

Dealing with a member whose email is bouncing

What can owner/mods do to help a member whose email is bouncing?

First, realize that groups.io can't fix it.¹ The member's email service provider is blocking delivery of emails from groups.io to the member. Until that block is removed by the service provider, no messages will get through to the member, including bounce probes.

To resolve bounces:

1. Go to the Members list (Admin->Members) and view the email delivery history bounce error messages ("Recent Bounces").²
   • 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.
2. Communicate those errors to tech support at the member's email service provider AS THEY ARE THE ONES DOING THE BLOCKING.
   • Generally the member will have to do this.
3. Wait until tech support at the member's email service provider says they have fixed their problem or whatever they are doing to block the email from groups.io.
4. Now send a bounce probe to see if the problem is really fixed. See this message on how to send a bounce probe.
5. It may help to tell the member what to watch for. You can send him/her the link to this example bounce probe message in our wiki.
6. If the bounce probe email is delivered and the member responds to the probe (clicks on the link in the email), groups.io will resume sending email to the member.
   

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. 

[1]: Sometimes an email provider will have groups.io listed on a "spam black list".  Support at groups.io might have to get in touch with the black list host and/or the email provider to straighten out the problem.  

[2]: The Recent Bounces list in your member's member record will display activity from your group only. With the understanding that his account's bouncing status could have originated from failed delivery of messages in a different group, you may have to direct him to look it up himself (https://groups.io/account?page=bounces) to get a full picture of what's going on.