MAIL is a lightweight Messaging Handling Service (MHS X.419).
> application:which_applications(). [{mail,"MAIL IPMS MHS Protocol","3.4"}, {syn,"SYN pub/sub", "1.5.0"}, {sh,"SH EXE REM SEC","3.5"}, {rocksdb,"RocksDB for Erlang","1.0.0"}, {mad,"MAD Manage Dependencies","5.4"}, {ssl,"Erlang/OTP SSL application","9.2.1"}, {cowlib,"COWLIB Web protocols.","2.6.0"}, {n2o,"N2O DAS MQTT TCP WebSocket","6.4"}, {kvs,"KVS Abstract Chain Database","6.4"}, {mnesia,"MNESIA CXC 138 12","4.15.6"}, {public_key,"Public key infrastructure","1.6.5"}, {crypto,"CRYPTO","4.4.1"}, {asn1,"The Erlang ASN1 compiler version 5.0.8","5.0.8"}, {stdlib,"ERTS CXC 138 10","3.8.1"}, {kernel,"ERTS CXC 138 10","6.3.1"}]