Gmail at least used to support sharing email URLs among the sender and recipients of an email, so long as they had Gmail accounts. (Nobody else could see them,

Gmail at least used to support sharing email URLs among the sender and recipients of an email, so long as they had Gmail accounts. (Nobody else could see them, naturally.) Useful for "...When did you send me that email?" "It's this email, <plink>." I haven't tried it in awhile, though.