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Isn't SMTP actually pretty resilient to outages? Typically sending mail servers will retry for hours (or even days) before giving up when a recipient server is

Isn't SMTP actually pretty resilient to outages? Typically sending mail servers will retry for hours (or even days) before giving up when a recipient server is down.

_asciiker_ 11y ago
Depends on the error the DNS handler 'name.nospy.so' would throw at it.
McElroy 11y ago
Yes. This is correct. Once, I had misconfigured my mail server when adding another domain I had bought and it rejected an e-mail. While I was looking into it, I saw in the logs that the sending party had retried after 15 minutes so I corrected my config and waited another 15 and I got the e-mail. Of course, number of retries, if any, and time between attempts will vary between different servers and their configs. Another story I have about e-mail is that another misconfiguration on my part caused mail from me to others to be spam filtered or outright dropped by some receivers. It wasn't until I attempted to send an e-mail to a Debian mailing list that I learned why that was. Their e-mail server was nice enough to reply with the exact reason why they would not accept my mail. I was then able to fix it. (Though I don't remember if they did so in the form of what was said over SMTP and seen by me in logs, or if they bounced the e-mail.)
bhauer 11y ago
Yes, it is. Virtually all normal SMTP servers will re-try e-mail delivery several times spaced over at least several hours before rejecting delivery with a notification back to the sender. I have run my own e-mail server for about 17 years, originally from my home and more recently from a data-center where I have co-located my server. Admittedly, when I had my mail server at my home, I would suffer outages long enough to miss e-mails when I needed to do something as severe as work on my home's electrical panel or move. But generally speaking, a momentary glitch in network connectivity would not result in lost e-mail. Since moving my server to a data-center, the only downtime I had was when I needed to replace a disk. As the above paragraph suggests, I am strongly in favor of people running their own mail servers and moving away from the presently-popular centralized Internet, back toward a decentralized model. This device isn't for me, and probably isn't for several of us here, but it's precisely the kind of thing I'd like to suggest to other people who would not otherwise be comfortable running a mail server. I know a lot of programmers who shiver at the thought of managing their own servers, and I feel that's a regretful situation for the Internet at large. It suggests two things: (a) many programmers fear servers, which I don't think is healthy and (b) insufficient R&D has gone into making infrastructure easier to manage. After all (a) is a rational fear given the state of the art in many cases. It can in fact be quite difficult to set up a mail server (although once setup, most are pretty hands-off). It should be much easier to navigate through the settings and have a nearly out-of-the-box configuration that is sane and avoids the most common pitfalls. Aside: Incidentally, I found that even mainstream ISPs like AT&T will unblock port 25 if you call them up and explain you are running your own personal mail server. When I moved to AT&T country, they did exactly that with no questions asked.
- fche 11y ago
  "Since moving my server to a data-center, the only downtime I had was when I needed to replace a disk." By the way, there exist backup MX services - commercial or self-made, which would give you 100% incoming-mail uptime but without having to move or copy your server to a data center.
  - bhauer 11y ago
    Thanks for the note! I'll definitely keep that in mind next time I evaluate my hosting environment. I expect to switch to a different data center eventually, and that would come in handy.
  - jlgaddis 11y ago
    Some hosts are doing away with backup MX hosts (including me/work) simply because a) any sane sender will retry for a period of at least several hours and b) sending via the backup MX is a common way for spammers to (attempt to) increase the chances of their mails getting delivered (e.g., due to lack of/decreased filtering on backup MX hosts).
- mbrock 11y ago
  Great comment. As for programmers fearing servers: all the mail servers I've tried are almost incredibly byzantine, making them stressful to configure and hard to understand. My brother got tired of this and wrote a functioning and mostly conformant SMTP server in less than 50 lines of bash (using djb's tcpserver and delivering to maildrop). As far as I'm concerned, all the configuration I can ever imagine needing for a simple SMTP server could be specified with like max 3 command line switches. So yeah, I think it is a somewhat rational fear, and I don't understand why everything seems so amazingly complex.
  - jlgaddis 11y ago
    FWIW, OpenSMTPD is extremely simple to configure and get up and running. (I don't use it other than as an "outbound-only sender" but the configuration file is very readable and simple).

Isn't SMTP actually pretty resilient to outages? Typically sending mail servers will retry for hours (or even days) before giving up when a recipient server is down.

_asciiker_ 11y ago

Depends on the error the DNS handler 'name.nospy.so' would throw at it.

McElroy 11y ago

Yes. This is correct. Once, I had misconfigured my mail server when adding another domain I had bought and it rejected an e-mail. While I was looking into it, I saw in the logs that the sending party had retried after 15 minutes so I corrected my config and waited another 15 and I got the e-mail. Of course, number of retries, if any, and time between attempts will vary between different servers and their configs. Another story I have about e-mail is that another misconfiguration on my part caused mail from me to others to be spam filtered or outright dropped by some receivers. It wasn't until I attempted to send an e-mail to a Debian mailing list that I learned why that was. Their e-mail server was nice enough to reply with the exact reason why they would not accept my mail. I was then able to fix it. (Though I don't remember if they did so in the form of what was said over SMTP and seen by me in logs, or if they bounced the e-mail.)

bhauer 11y ago

Yes, it is. Virtually all normal SMTP servers will re-try e-mail delivery several times spaced over at least several hours before rejecting delivery with a notification back to the sender. I have run my own e-mail server for about 17 years, originally from my home and more recently from a data-center where I have co-located my server. Admittedly, when I had my mail server at my home, I would suffer outages long enough to miss e-mails when I needed to do something as severe as work on my home's electrical panel or move. But generally speaking, a momentary glitch in network connectivity would not result in lost e-mail. Since moving my server to a data-center, the only downtime I had was when I needed to replace a disk. As the above paragraph suggests, I am strongly in favor of people running their own mail servers and moving away from the presently-popular centralized Internet, back toward a decentralized model. This device isn't for me, and probably isn't for several of us here, but it's precisely the kind of thing I'd like to suggest to other people who would not otherwise be comfortable running a mail server. I know a lot of programmers who shiver at the thought of managing their own servers, and I feel that's a regretful situation for the Internet at large. It suggests two things: (a) many programmers fear servers, which I don't think is healthy and (b) insufficient R&D has gone into making infrastructure easier to manage. After all (a) is a rational fear given the state of the art in many cases. It can in fact be quite difficult to set up a mail server (although once setup, most are pretty hands-off). It should be much easier to navigate through the settings and have a nearly out-of-the-box configuration that is sane and avoids the most common pitfalls. Aside: Incidentally, I found that even mainstream ISPs like AT&T will unblock port 25 if you call them up and explain you are running your own personal mail server. When I moved to AT&T country, they did exactly that with no questions asked.

fche 11y ago
"Since moving my server to a data-center, the only downtime I had was when I needed to replace a disk." By the way, there exist backup MX services - commercial or self-made, which would give you 100% incoming-mail uptime but without having to move or copy your server to a data center.
- bhauer 11y ago
  Thanks for the note! I'll definitely keep that in mind next time I evaluate my hosting environment. I expect to switch to a different data center eventually, and that would come in handy.
- jlgaddis 11y ago
  Some hosts are doing away with backup MX hosts (including me/work) simply because a) any sane sender will retry for a period of at least several hours and b) sending via the backup MX is a common way for spammers to (attempt to) increase the chances of their mails getting delivered (e.g., due to lack of/decreased filtering on backup MX hosts).
mbrock 11y ago
Great comment. As for programmers fearing servers: all the mail servers I've tried are almost incredibly byzantine, making them stressful to configure and hard to understand. My brother got tired of this and wrote a functioning and mostly conformant SMTP server in less than 50 lines of bash (using djb's tcpserver and delivering to maildrop). As far as I'm concerned, all the configuration I can ever imagine needing for a simple SMTP server could be specified with like max 3 command line switches. So yeah, I think it is a somewhat rational fear, and I don't understand why everything seems so amazingly complex.
- jlgaddis 11y ago
  FWIW, OpenSMTPD is extremely simple to configure and get up and running. (I don't use it other than as an "outbound-only sender" but the configuration file is very readable and simple).