filesystems aren't widely available. Solution: Keep a journal, separatefrom the queue, adequate to rebuild the queue (with at worst someduplicate deliveries). Compress the journal. This would dramaticallyreduce total disk I/O.Bounce aggregation is a dubious feature. Bounce records aren'tcrashproof; there can be a huge delay between a failure and a bounce;the resulting bounce format is unnecessarily complicated. I'm tempted toscrap the bounce directory and send one bounce for each failingrecipient, with appropriate modifications in the accompanying text.qmail-stop implementation: setuid to UID_SEND; kill -TERM -1. Or runqmail-start under an external service controller, such as supervise;that's why it runs in the foreground.The readdir() interface hides I/O errors. Lower-level interfaces wouldlead me into a thicket of portability problems. I'm really not sure whatto do about this. Of course, a hard I/O error means that mail is toast,but a soft I/O error shouldn't cause any trouble.job_open() or pass_dochan() could be paranoid about the same id,channelalready being open; but, since messdone() is so paranoid, the worstpossible effect of a bug along these lines would be double delivery.Mathematical amusement: The optimal retry schedule is essentially,though not exactly, independent of the actual distribution of messagedelay times. What really matters is how much cost you assign to retriesand to particular increases in latency. qmail's current quadratic retryschedule says that an hour-long delay in a day-old message is worth thesame as a ten-minute delay in an hour-old message; this doesn't seem sounreasonable.Insider information: AOL retries their messages every five minutes forthree days straight. Hmmm.6. Sending mail through the network (qmail-rspawn, qmail-remote)Are there any hosts, anywhere, whose mailers are bogged down by hugemessages to multiple recipients at a single host? For typical hosts,multiple RCPTs per SMTP aren't an ``efficiency feature''; they're a_slowness_ feature. Separate SMTP transactions have much lower latency.I've heard three complaints about bandwidth use from masochists sendingmessages through a modem through a smarthost to thousands of users---without sublists! They can get much better performance with QMQP.In the opposite direction: It's tempting to remove the @host part of theqmail-remote recip argument. Or at least avoid double-dns_cname.There are lots of reasons that qmail-rspawn should take a more activerole in qmail-remote's activities. It should call separate programs todo (1) MX lookups, (2) SMTP connections, (3) QMTP connections. (But thiswouldn't be so important if the DNS library didn't burn so much memory.)I bounce ambiguous MXs. (An ``ambiguous MX'' is a best-preference MXrecord sending me mail for a host that I don't recognize as local.)Automatically treating ambiguous MXs as local is incompatible with mydesign decision to keep local delivery working when the network goesdown. It puts more faith in DNS than DNS deserves. Much better: Haveyour MX records generated automatically from control/locals.If I successfully connect to an MX host but it temporarily refuses toaccept the message, I give up and put the message back into the queue.But several documents seem to suggest that I should try further MXrecords. What are they thinking? My approach deals properly with downedhosts, hosts that are unreachable through a firewall, and loadbalancing; what else do people use multiple MX records for?Currently qmail-remote sends data in 1024-byte buffers. Perhaps itshould try to take account of the MTU.Perhaps qmail-remote should allocate a fixed amount of DNS/connect()time across any number of MXs; this idea is due to Mark Delany.RFC 821 doesn't say what it means by ``text.'' qmail-remote assumes thatthe server's reply text doesn't contain bare LFs.RFC 821 and RFC 1123 prohibit host names in MAIL FROM and RCPT TO frombeing aliases. qmail-remote, like sendmail, rewrites aliases in RCPT;people who don't list aliases in control/locals or sendmail's Cw areimplicitly relying on this conversion. It is course quite silly for aninternal DNS detail to have such an effect on mail delivery, but that'show the Internet works. On the other hand, the compatibility argumentsdo not apply to MAIL FROM. qmail-remote no longer bothers with CNAMElookups for the envelope sender host.7. Delivering mail locally (qmail-lspawn, qmail-local)qmail-local doesn't support comsat. comsat is a pointless abomination.Use qbiff if you want that kind of notification.The getpwnam() interface hides I/O errors. Solution: qmail-pw2u.8. sendmail V8's new featuressendmail-8.8.0/doc/op/op.me includes a list of big improvements ofsendmail 8.8.0 over sendmail 5.67. Here's how qmail stacks up againsteach of those improvements. (Of course, qmail has its own improvements,but that's not the point of this list.)Connection caching, MX piggybacking: Nope. (Profile. Don't speculate.)Response to RCPT command is fast: Yup.IP addresses show up in Received lines: Yup.Self domain literal is properly handled: Yup.Different timeouts for QUIT, RCPT, etc.: No, just a single timeout.Proper <> handling, route-address pruning: Yes, but not configurable.ESMTP support: Yup. (Server-side, including PIPELINING.)8-bit clean: Yup. (Including server-side 8BITMIME support; same assendmail with the 8 option.)Configurable user database: Yup.BIND support: Yup.Keyed files: Yes, in fastforward.931/1413/Ident/TAP: Yup.Correct 822 address list parsing: Yup. (Note that sendmail still hassome major problems with quoting.)List-owner handling: Yup.Dynamic header allocation: Yup.Minimum number of disk blocks: Yes, via tunefs -m. (Or quotas; the rightsetup has qmailq with a small quota, qmails with a larger quota, so thatqmail-send always has room to work.)Checkpointing: Yes, but not configurable---qmail always checkpoints.Error message configuration: Nope.GECOS matching: Not directly, but easy to hook in.Hop limit configuration: No. (qmail's limit is 100 hops. qmail offersautomatic loop protection much more advanced than hop counting.)MIME error messages: No. (qmail uses QSBMF error messages, which aremuch easier to parse.)Forward file path: Yes, via /etc/passwd.Incoming SMTP configuration: Yes, via inetd or tcpserver.Privacy options: Yes, but they're not options.Best-MX mangling: Nope. See section 6 for further discussion.7-bit mangling: Nope. qmail always uses 8 bits.Support for up to 20 MX records: Yes, and more. qmail has no limitsother than memory.Correct quoting of name-and-address headers: Yup.VRFY and EXPN now different: Nope. qmail always hides this information.Multi-word classes, deferred macro expansion, separate envelope/header$g processing, separate per-mailer envelope and header processing, newcommand line flags, new configuration lines, new mailer flags, newmacros: These are sendmail-specific; they wouldn't even make sense forqmail. For example, _of course_ qmail handles envelopes and headersseparately; they're almost entirely different objects!9. Miscellanysendmail-clone and qsmhook are too bletcherous to be documented. (Theofficial replacement for qsmhook is preline, together with theqmail-command environment variables.)I've considered making install atomic, but this is very difficult to doright, and pointless if it isn't done right.RN suggests automatically putting together a reasonable set of lines for/etc/passwd. I perceive this as getting into the adduser business, whichis worrisome: I'll be lynched the first time I screw up somebody'spasswd file. This should be left to OS-specific installation scripts.The BSD 4.2 inetd didn't allow a username. I think I can safely forgetabout this. (DS notes that the username works under Ultrix even thoughit's undocumented.)I should clean up the bput/put choices.Some of the stralloc_0()s indicate that certain lower-level routinesshould grok stralloc.qmail assumes that all times are positive; that pid_t, time_t and ino_tfit into unsigned long; that gid_t fits into int; that the character setis ASCII; and that all pointers are interchangeable. Do I care?The bat book justifies sendmail's insane line-splitting mechanism bypointing out that it might be useful for ``a 40-character brailleprint-driving program.'' C'mon, guys, is that your best excuse?qmail's mascot is a dolphin.