Editing UUCP (section)

==Mail routing==
[[File:UUCP Email Address .jpg|thumb | Business card with UUCP email address]]
The {{code|uucp}} and {{code|uuxqt}} capabilities could be used to send [[email]] between machines, with suitable mail user interfaces and delivery agent programs.  A simple UUCP mail address was formed from the adjacent machine name, an [[exclamation mark]] (often pronounced ''bang''), followed by the user name on the adjacent machine.  For example, the address ''barbox!user'' would refer to user ''user'' on adjacent machine ''barbox''.<ref>{{cite mailing list |url=https://mailarchive.ietf.org/arch/msg/irtf-discuss/DWOvH0uMV29sBxZ6rcrZgrQC-ow/ |title=[Internet Policy] Why the World Must Resist Calls to Undermine the Internet |date=20 March 2022 |access-date=24 March 2022 |mailing-list=IETF-Discussion |first=Vint |last=Cerf |author-link=Vint Cerf}}</ref>

Mail could furthermore be routed through the network, traversing any number of intermediate nodes before arriving at its destination.  Initially, this had to be done by specifying the complete path, with a list of intermediate host names separated by bangs.  For example, if machine ''barbox'' is not connected to the local machine, but it is known that ''barbox'' is connected to machine ''foovax'' which does communicate with the local machine, the appropriate address to send mail to would be ''foovax!barbox!user''.

User ''barbox!user'' would generally publish their UUCP email address in a form such as ''…!bigsite!foovax!barbox!user''.  This directs people to route their mail to machine ''bigsite'' (presumably a well-known and well-connected machine accessible to everybody) and from there through the machine ''foovax'' to the account of user ''user'' on ''barbox''. Publishing a full path would be pointless, because it would be different, depending on where the sender was. (e.g. Ann at one site may have to send via path ''gway!tcol!canty!uoh!bigsite!foovax!barbox!user'', whereas from somewhere else, Bill has to send via the path ''pdp10!router22!bigsite!foovax!barbox!user''). Many users would suggest multiple routes from various large well-known sites, providing even better and perhaps faster connection service from the mail sender.

===Bang path===
An email address of this form was known as a '''bang path'''.
Bang paths of eight to ten machines (or ''hops'') were not uncommon in 1981, and late-night dial-up UUCP links could cause week-long transmission times. Bang paths were often selected by both transmission time and reliability, as messages would often get lost.  Some hosts went so far as to try to "[[Rewriting|rewrite]]" the path, sending mail via "faster" routes—this practice tended to be frowned upon.

The "pseudo-domain" ending '''[[.uucp]]''' was sometimes used to designate a hostname as being reachable by UUCP networking, although this was never formally registered in the [[domain name system]] (DNS) as a [[top-level domain]].  The uucp community administered itself and did not mesh well with the administration methods and regulations governing the DNS; .uucp works where it needs to{{where|date=January 2017}}; some hosts{{which|date=January 2017}} punt mail out of SMTP queue into uucp queues on gateway machines if a .uucp address is recognized on an incoming SMTP connection.{{citation needed|date=January 2017}}

[[Usenet]] traffic was originally transmitted over the UUCP protocol, typically over dialup modems. At each receiving node, each Usenet article's ''Path'' header line would have the current node's name prepended to the path, separated by "!".  For example, an article that came in from node ''utzoo'' to node ''decvax'' with ''Path: [[Henry Spencer|utzoo!henry]]'' would have that line change to ''Path: decvax!utzoo!henry'').  Usenet software would then send a copy of each article to every neighbor node which had been configured to receive the newsgroup(s) that the article had been posted to -- unless that neighbor was already in the ''Path'' line.  These paths were thus used to ensure that articles did not "loop" back to a node that already had them.

In general, like other [[Non-Internet email address|older e-mail address formats]], bang paths have now been superseded by the "[[Email address#Syntax|@ notation]]", even by sites still using UUCP.  A UUCP-only site can register a DNS domain name, and have the DNS server that handles that domain provide [[MX record]]s that cause Internet mail to that site to be delivered to a UUCP host on the Internet that can then deliver the mail to the UUCP site.