From b732a73bc773789894466b0e5320b2f1fe42c7e9 Mon Sep 17 00:00:00 2001 From: John Denker Date: Fri, 1 Jun 2012 18:58:45 -0700 Subject: original, as downloaded from http://www.qmail.org/netqmail-1.06.tar.gz --- addresses.5 | 260 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 260 insertions(+) create mode 100644 addresses.5 (limited to 'addresses.5') diff --git a/addresses.5 b/addresses.5 new file mode 100644 index 0000000..1fd4c5b --- /dev/null +++ b/addresses.5 @@ -0,0 +1,260 @@ +.TH addresses 5 +.SH "NAME" +addresses \- formats for Internet mail addresses +.SH "INTRODUCTION" +A +.B mail address +is a string of characters containing @. + +Every mail address has a +.B local part +and a +.B domain part\fR. +The domain part is everything after the final @. +The local part is everything before. + +For example, the mail addresses + +.EX + God@heaven.af.mil + @heaven.af.mil + @at@@heaven.af.mil +.EE + +all have domain part +.BR heaven.af.mil . +The local parts are +.BR God , +empty, +and +.BR @at@ . + +Some domains have owners. +It is up to the owner of +.B heaven.af.mil +to say how mail messages will be delivered to addresses with domain part +.BR heaven.af.mil . + +The domain part of an address is interpreted without regard to case, so + +.EX + God@heaven.af.mil +.br + God@HEAVEN.AF.MIL +.br + God@Heaven.AF.Mil +.EE + +all refer to the same domain. + +There is one exceptional address that does not contain an @: +namely, the empty string. +The empty string cannot be used as a recipient address. +It can be used as a sender address so that +the real sender doesn't receive bounces. +.SH "QMAIL EXTENSIONS" +The +.B qmail +system allows several further types of addresses in mail envelopes. + +First, an envelope recipient address without an @ is interpreted as being at +.IR envnoathost . +For example, if +.I envnoathost +is +.BR heaven.af.mil , +the address +.B God +will be rewritten as +.BR God@heaven.af.mil . + +Second, the address +.B #@[] +is used as an envelope sender address for double bounces. + +Third, envelope sender addresses of the form +.I pre\fB@\fIhost\fB-@[] +are used to support variable envelope return paths (VERPs). +.B qmail-send +will rewrite +.I pre\fB@\fIhost\fB-@[] +as +.I prerecip\fB=\fIdomain\fB@\fIhost +for deliveries to +.IR recip\fB@\fIdomain . +Bounces directly from +.B qmail-send +will come back to +.IR pre\fB@\fIhost . +.SH "CHOOSING MAIL ADDRESSES" +Here are some suggestions on choosing mail addresses for the Internet. + +Do not use non-ASCII characters. +Under RFC 822 and RFC 821, +these characters cannot be used in mail headers or in SMTP commands. +In practice, they are regularly corrupted. + +Do not use ASCII control characters. +NUL is regularly corrupted. +CR and LF cannot be used in some combinations +and are corrupted in all. +None of these characters are usable on business cards. + +Avoid spaces and the characters + +.EX + \\"<>()[],;: +.EE + +These all require quoting in mail headers and in SMTP. +Many existing mail programs do not handle quoting properly. + +Do not use @ in a local part. +@ requires quoting in mail headers and in SMTP. +Many programs incorrectly look for the first @, +rather than the last @, +to find the domain part of an address. + +In a local part, +do not use two consecutive dots, a dot at the beginning, or a dot at the end. +Any of these would require quoting in mail headers. + +Do not use an empty local part; it cannot appear in SMTP commands. + +Avoid local parts longer than 64 characters. + +Be wary of uppercase letters in local parts. +Some mail programs (and users!) will incorrectly convert +.B God@heaven.af.mil +to +.BR god@heaven.af.mil . + +Be wary of the following characters: + +.EX + $&!#~`'^*|{} +.EE + +Some users will not know +how to feed these characters safely to their mail programs. + +In domain names, stick to letters, digits, dash, and dot. +One popular DNS resolver has, +under the banner of security, +recently begun destroying domain names +that contain certain other characters, +including underscore. +Exception: A dotted-decimal IP address in brackets, +such as +.BR [127.0.0.1] , +identifies a domain owned by whoever owns the host at that IP address, +and can be used safely. + +In a domain name, +do not use two consecutive dots, +a dot at the beginning, +or a dot at the end. +This means that, +when a domain name is broken down into components separated by dots, +there are no empty components. + +Always use at least one dot in a domain name. +If you own the +.B mil +domain, +don't bother using the address +.BR root@mil ; +most users will be unable to send messages to that address. +Same for the root domain. + +Avoid domain names longer than 64 characters. +.SH "ENCODED ADDRESSES IN SMTP COMMANDS" +RFC 821 defines an encoding of mail addresses in SMTP. +For example, the addresses + +.EX + God@heaven.af.mil +.br + a"quote@heaven.af.mil +.br + The Almighty.One@heaven.af.mil +.EE + +could be encoded in RCPT commands as + +.EX + RCPT TO: +.br + RCPT TO: +.br + RCPT TO: +.EE + +There are several restrictions in RFC 821 +on the mail addresses that can be used over SMTP. +Non-ASCII characters are prohibited. +The local part must not be empty. +The domain part must be a sequence of elements separated by dots, +where each element is either a component, +a sequence of digits preceded by #, +or a dotted-decimal IP address surrounded by brackets. +The only allowable characters in components are +letters, digits, and dashes. +Every component must (believe it or not) +have at least three characters; +the first character must be a letter; +the last character must not be a hyphen. +.SH "ENCODED ADDRESSES IN MAIL HEADERS" +RFC 822 defines an encoding of mail addresses +in certain header fields in a mail message. +For example, the addresses + +.EX + God@heaven.af.mil +.br + a"quote@heaven.af.mil +.br + The Almighty.One@heaven.af.mil +.EE + +could be encoded in a +.B To +field as + +.EX + To: God@heaven.af.mil, +.br + <@brl.mil:"a\\"quote"@heaven.af.mil>, +.br + "The Almighty".One@heaven.af.mil +.EE + +or perhaps + +.EX + To: < "God"@heaven .af.mil>, +.br + "a\\"quote" (Who?) @ heaven . af. mil +.br + , God<"The Almighty.One"@heaven.af.mil> +.EE + +There are several restrictions on the mail addresses that can +be used in these header fields. +Non-ASCII characters are prohibited. +The domain part must be a sequence of elements separated by dots, +where each element either (1) begins with [ and ends with ] +or (2) is a nonempty string of printable ASCII characters +not including any of + +.EX + \\".<>()[],;: +.EE + +and not including space. +.SH "SEE ALSO" +envelopes(5), +qmail-header(5), +qmail-inject(8), +qmail-remote(8), +qmail-smtpd(8) -- cgit v1.2.3