Had an iCloud user accept an Invite From Disroot's NextCloud and their acceptance email, bounced [550 5.7.1 Command rejected (in reply to end of DATA command)]
Ive done some testing and this appears to be specific to accepting invitations in Mail.app ( macOS Apple Mail) on iCloud.
Had an iCloud user accept an Invite From Disroot's NextCloud and their acceptance email, bounced [550 5.7.1 Command rejected (in reply to end of DATA command)]
So your saying Apple Mail, likely botched the date field in the head header?
Had an iCloud user accept an Invite From Disroot's NextCloud and their acceptance email, bounced [550 5.7.1 Command rejected (in reply to end of DATA command)]