AOL accidentally hard bounces valid mail

Last night (Mar 29, 2017) between about 8pm Eastern and 9:30pm Eastern AOL suffered a technical issue. Every email sent to them received a “Recipient address rejected” reply.  One example of the error message:
Mar 29 20:45:12 p2-lvmail11 lsb1-99-208-250/smtp[22251]: A88DFC2DBE9: to=<redacted@aol.com>, relay=mailin-01.mx.aol.com[64. 12.91.195]:25, delay=0.18, delays=0.01/0/0.14/0.03, dsn=5.1.1, status=bounced (host mailin-01.mx.aol.com[64.12.91. 195] said: 550 5.1.1 <redacted@aol.com>: Recipient address rejected: aol.com (in reply to RCPT TO command))
The issue was brought to AOLs attention and things were fixed rapidly after that. An AOL representative has stated that these were invalid replies and that addresses do not need to be removed from future emails.
Most of the ESPs are aware of this and are working to restore any bounced addresses to their users. At some places this requires manual intervention, so it’s taking some time to get all the addresses restored.
This is one of the reasons that our best bounce handling recommendations are not to remove an address for a single bounce – sometimes the ISPs have technical problems. Like the time a routing failure meant a major ISPs MX machines couldn’t reach their authentication servers to get the list of active users. Or the time all an ISPs MXs were removed from DNS. A lot of the internet is still managed manually, and despite extensive safeguards put in place bad things can, and do, still happen. Usually these problems are resolved quickly and mail starts flowing again.
Morning advice: Do not deactivate addresses that bounced at AOL last night.