In Germany, where I work, it is usual at the end of employement to ask for a letter of recommendation ("Zeugnis") that lists the tasks performed, and how good the employee was. It is an important document, as it will typcally be required when applying for jobs. Obviously, no employee would accept a document explicitly stating "this guy is a lazy bastard, do not hire him", so there is a "Zeugnissprache", a "secret code" to disguise this information as praise. One part of this code is that a missing period in the last sentence means "please ignore everything said here, this guy is horrible".
How do I know? I let a lawyer check my Zeugnis after my last employment, and (I assume out of lack of care, as all my performance reviews were positive) the last sentence was missing the period.
You just use the mail program from mailutils or whatever.
Just from a point of view of deliverability, developing bare bones SMTP interaction over a socket is a nonstarter. You can't just connect to random mail exchange hosts directly and send mail these days. A solution has to be capable of connecting to a specific SMTP forwarding host (e.g. provided by your ISP). For that, you need to implement connections over TLS, with authentication and all.
Also, a slightly ironic thing is that cron already knows how to send mail. The output of a cron job is mailed to the owner. Some crons let that mail address be overriden with a MAILTO variable in the crontab or some such thing.
But the other thing is: Don’t vendor your dependencies. Those libraries you use need to be updated regularly and timely, and absolutely not “only as necessary”. If updates lag behind or are avoided entirely, bugs like this can be huge problems even when the upstream code has been fixed, for people who thought that they should update only when they, themselves, see a problem or need.
Relatedly, escaping somehow seems to be a foreign concept for a lot of programmers, who wouldn't ever see the above situation and ask themselves "but what if I want to send an email with a line containing a single dot?" yet another large group of them finds it perfectly logical and easy to understand.
SMTP https://www.rfc-editor.org/rfc/rfc5321#section-4.5.2
Also in POP3 https://www.rfc-editor.org/rfc/rfc1939#page-8
As soon as I printed them, the error was clear. My version ran to two pages and the good implementation one page. I had not been careful to clear the buffer before sending the data (mbufs don't you know).
This still cracks me up.
... lots of text ... <br>We are happy to welcome you to our family.<br>
As soon as I read the above, I knew the below would be the result.
> It seems one of our other teams haven't gotten around to patching this bug in their code.
What the...
;-)
Other than the obvious moral that protocols should be implemented properly, the moral of the story is that all abstractions are leaky, and it will always be useful to understand the lower levels.
Of course if it was modern, different question.
Why is it implemented that way?
If a single period means end of mail then more than a period means it's mail data.
Why deleting the period in the first place? Couldn't they store one byte to check the next?
there's a secondary issue here, why in the world would you auto split a monetary value across a numeric decimal indicator? why would you split lines at all for this use case?
ironically titled..
Good luck having it handle any of the SMTP craziness that isn't on the short introduction to the protocol.
Not to mention all the weird bandaids on top of bandaids to try to get sender verification and tamper proof emails working. That alongside the complete lack of end to end encryption.
It's just an incredibly unpleasant tech stack from top to bottom, through and through. The amount of moving parts/pieces of running software needing to cooperate just right to even function as a simple outgoing-only mail server is too damn high.
- The SMTP client spec says that an additional period would be added here.
- The SMTP server spec says that it would remove this additional period, bringing us back to one period.
I don’t get how this led to there being no period at all. Am I missing something?
If I wanted to root cause this, the real problem is right there. Implementing protocols correctly is hard and bugs like in the post are common. A properly implemented SMTP client library, like one you would pull off the shelf, would accept text and encode it properly per the SMTP protocol, regardless of where the periods were in the input. The templating layer shouldn't be worrying about SMTP.