From Handwiki - Reading time: 1 minIBMMAIL was an email gateway service owned and operated by IBM for running email services (terminal hosted) on IBM Mainframe computers. It supported both X.400 and SMTP based email communications and also attachments in both EBCDIC and ASCII formats.
The service automatically generated email addresses for users, by combining a two letter country code where the mainframe is located, and appending six random characters.