A recent question Introductory Books easier than Dover tempted me to answer with my own books (How To Fold It, Pop-Up Geometry). But I did not, because it seems best to avoid such "advertising." Is this correct?

Meanwhile I wrote directly to the OP, whose profile included his email address.

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    $\begingroup$ Our SE overlords would prefer that all contact on the site be mitigated through the site. The given reason is that if things escalate, we can do nothing about what happens off-site. That being said, we are all professionals here, this other user has put their email in their profile, and you are likely well aware of the risks and benefits of reaching out via email. Personally, with my moderator hat off, contacting someone via email seems reasonable. The only downside I see is that whatever answer you give via email is not available to others. $\endgroup$
    – Xander Henderson Mod
    Jan 6, 2023 at 15:15
  • $\begingroup$ @XanderHenderson. Thanks. The OP and I had a cordial exchange. $\endgroup$ Jan 7, 2023 at 1:15
  • $\begingroup$ Excellent. I am glad it all worked out. :D $\endgroup$
    – Xander Henderson Mod
    Jan 7, 2023 at 1:36

1 Answer 1


The relevant help page for this kind of question is How to not be a spammer.

The key point is to answer the question and avoid undisclosed unrelated and possibly excessive self-promotion, but if your books are relevant to the question, and you explain the reasons and disclose the authorship, it's perfectly acceptable to refer to them.

Around the Stack Exchange sites you may find various legit examples of self-promotion.

I'd avoid, instead, directly contacting a user to answer a question, even when they include their email address.

  • $\begingroup$ Thanks, Massimo, I appreciate the advice. My only question is why should I not contact the OP directly when their email address is in their profile? $\endgroup$ Jan 2, 2023 at 19:05
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    $\begingroup$ @JosephO'Rourke The main reason is that should an argument ensue, however remote the possibility, moderators wouldn’t be able to help. $\endgroup$ Jan 2, 2023 at 19:17
  • $\begingroup$ This is the "correct" answer. You are more than welcome to recommend your own books (you are even encouraged to do so, when they are relevant). Just make sure that you make it clear that you are the author. $\endgroup$
    – Xander Henderson Mod
    Jan 6, 2023 at 15:13
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    $\begingroup$ @JosephO'Rourke " My only question is why should I not contact the OP directly when their email address is in their profile?" You obviously can do that (at your own risk). As a person, who is contacted quite regularly in private after an answer on MO (even though my e-mail is not listed on my profile page), I can say that "an argument" has never ensued (30+ encounters), I haven't always answered and feel no real obligation to answer (though usually do), and there have been several cases with mathematically interesting developments, but that is just my personal statistics :-) $\endgroup$
    – fedja
    Mar 22, 2023 at 18:09

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