How to isolate and retire toxic mailboxes?

When individual mailboxes become toxic, isolating and retiring them protects other sending infrastructure.

Identification:

Track metrics per mailbox, not just per campaign

Watch for mailboxes with higher bounce or complaint rates

Check individual mailbox reputation where possible

Note mailboxes triggering rate limits

Isolation steps:

Remove problematic mailbox from active campaigns

Stop warmup activity for that mailbox

Don't shift its volume to other accounts (spreads problems)

Document the issue and timeline

Investigation:

What campaigns ran through this mailbox?

What lists were contacted?

Any authentication or technical issues?

Pattern of complaints or blocks?

Retirement process:

Plan replacement mailbox before full retirement

Allow new mailbox to warm before needing it

Transfer any legitimate contacts if appropriate

Keep retired mailbox active to receive replies

Don't delete until reply handling is complete

Prevention:

Rotate mailboxes to avoid overuse

Monitor individual account health

Set lower limits on newer accounts

Have replacement accounts warming in reserve