I've seen at as well when sending out update emails from GAE or even SendGrid:
Often times there were special characters in the mail address, spaces before or after the email address, or some other almost unnoticeable typos. It's also possible that hotmail has routing issues or something, but I don't know if there's a way to find out. >From MS themselves: 9 times out of 10, this is the same as "mailbox not found". That other 10% of the time it could mean that there's a problem with your recipients account. Check to make sure that you have the e-mail address correct, wait a while and try again. If it still bounces, try contacting the recipient some other way. This means that your message is intentionally blocked because the receiving system thinks that the mail server you're using is a source of spam. Contact the support team of recipient's e-mail provider and request to have your account or domain unblocked. Not sure if has something to do with DNS resolution On Fri, 20 Oct 2017 at 03:52 PK <[email protected]> wrote: > Has anybody else experienced something similar, the message is of the form > below. Any suggestions where to start? It seems like an issue on the > Microsoft side but it happens only for e-mails originating at GAE standard. > > Your message wasn't delivered to [email protected] > <[email protected]> because the address couldn't be found. Check > for typos or unnecessary spaces and try again. > > > The response from the remote server was: > 550 5.5.0 Requested action not taken: mailbox unavailable. > > or > > 550 5.7.66 Requested action not taken: mailbox unavailable [HE1EUR02FT020. > eop-EUR02.prod.protection.outlook.com] > > -- > You received this message because you are subscribed to the Google Groups > "Google Cloud Insiders" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to > [email protected]. > Visit this group at https://groups.google.com/group/google-cloud-insiders. > To view this discussion on the web visit > https://groups.google.com/d/msgid/google-cloud-insiders/EEF05F0C-1D9A-44D8-9839-439F16309029%40gae123.com > <https://groups.google.com/d/msgid/google-cloud-insiders/EEF05F0C-1D9A-44D8-9839-439F16309029%40gae123.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/CAKkrQ9s%3D8L8cPpkcE4izZsRjOeHV%2BJauAyBFP-MBqdxZv0QVOg%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
