Secure email service Tutanota is being blocked by AT&T in parts of the United States.
To be clear: AT&T do not say or suggest that they are intentionally blocking it, and nobody has provided proof to the contrary.
#Routing issues happen all the time and that is the most plausible explanation.
A #traceroute would be as good a place to start as any.
A Mastodon instance for info/cyber security-minded people.