Suppose one is seeking external comments on the quality of one's research for a tenure/promotion file. Assume that my institution requires such a letter and my chair has advised me that "it would be desirable to have an outside expert comment on the quality of this paper."
What about contacting experts in the field who you don't know and asking them to write a letter about one of your papers? Has anyone ever done that? Is it highly unusual? Or even rude or a cultural faux-pas?
Also, does it matter whether the manuscript is in draft form or already published (or in-between)?
Maybe the answer will be field-dependent (and more generally culture-dependent)? I am in math and in the USA.
I understand that, generally, one would ideally have a large research network to call upon for such things, but I do not. Furthermore, my recent work is in a subfield where I simply do not know anyone with relevant expertise.
For clarity, I am at a teaching institution where the research requirement is quite minimal, but it is still valuable to get external expert comments.
Obviously people are busy, and there is a high chance that such a request would go unnoticed or ignored. That's fine.
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Edit: Given the comments and answers, it appears that my institution is quite distinct from the vast majority on this. I think there is a standard for the institution to seek such evaluations of a candidate which are essentially anonymous to the tenure/promotion candidate. This is not the kind of evaluation I am seeking. I am just seeking, e.g., evaluation of the quality of a specific paper. This is quite distinct from the more general anonymous evaluations of candidates which occurs at research-focused institutions.
The general consensus is that I should not contact those who I have no personal connection to and make such a request. I should at least have the department chair do that.