Similar to 宇宙からメリークリスマス

Biff (Unix)

Distributed Sender Blackhole List

GNU Mailman

Google Groups

HTML email

.mail

Maildir

Mailto

Mbox

MDaemon

MAPI

MX record

POPFile

Riseup

S/MIME

Sieve (mail filtering language)

Sympa

Tuta (email)

VCard

X-Face

X.400

AppleSingle and AppleDouble formats

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