A considerable portion of emails that I send to professors abroad to see if they have any position available remains unanswered. Not receiving a response, I can not imagine if they didn't attract to my CV or they simply forgot to open my email. In this way, I am wondering if it is normal(not rude) in academia to use email tracking softwares that inform you when the receiver opened your email. Actually, It is not very hard for them to check if the sender has used such software specially if they block the images in their received emails.
My sense is that the vast majority would not notice one way or another but that some potential advisors might and would find it intrusive and and inappropriate. In many other cases, (like myself) professors use text-based email clients or systems that that block this kind of tracking. In these cases, folks won't think you're rude but you still won't know if I've read it. For that matter, I may have opened an email but not read it carefully. In some cases, people will notice and and think it is rude or unethical.
Critically though, I can't see why knowing whether your email was opened will help.
The reality is that many professors receive between dozens and thousands (really!) of emails from prospective students. This has been discussed at length. Many answers on this site explain why it's just not possible for everybody to reply to every email and there are many reasons why people do not. They might not reply because they are overwhelmed by teaching. They might not reply because it's simply not a good match. They might not reply because they don't have funding to take on new students this year.
My advice is to pick a small number of perfect potential supervisors. Read their papers. Write emails that make it clear that you're not just mass-emailing anybody you can find but that you want to work with them. Send an email. If you want, send a follow-up after a week or so. In either case, I don't see how knowing that the email has been opened helps.
I guess the underlying assumption is that the sender is entitled to consideration and/or an answer, and so OP is trying to enforce this entitlement.
In email correspondence (academic or not), this assumption is usually wrong unless there is an established relationship (eg within a company), and trying to force it is indeed considered rude - or even intrusive/threatening.
I guess most people won't care about or notice the tracking (after all, we are OK that virtually every website tells Google about each web page we open), but if your e-mail happens to trigger an alert in their mailer or anti-virus, it won't do you any good.
It should be noted that e-mail tracking techniques are spectacularly bad at their primary purpose: reporting whether an e-mail has been read. Some people (like myself) configure their mail clients to never fetch online content, so you'll never see the notification. Other configurations may result in images being automatically downloaded, so you'll see a false positive.
I had used them since I began the applying process, however, today, in a telegram group that guys who are applying to Canadian universities exchange their experiences, several people said after they decided to stop using these kinds of trackers they have better responses. One guy said that his emails sent to spam inbox and another one copied an email from a professor who said: "I figured out that you use email tracker and suggest to unable this before contacting other faculties. Most of the professors find it an invasion of their privacy, and we never accept a student who uses such a program." As a student who has used this way for months, I don't suggest you apply trackers either. They are useless. It will not help you to find out if a professor has read your mail or not. Furthermore, you can never be sure because many professors use blockers. It isn't worth to use to even one potential supervisor by using these trackers.
A considerable portion of emails that I send to professors abroad to see if they have any position available remains unanswered. Not receiving a response, I can not imagine if they didn't attract to my CV or they simply forgot to open my email.
What difference does that make to you? Do you react an differently to the two? If so, please specify how, and we maybe be able to help you better.
My advice is simply to keep your own records, manually. That way, you will probably get a more exact record (it will certainly be in exactly the format which you prefer), and you do not risk offending anyone.
Suppose, that I (total stranger to you), would hack into your computer, circumvait your protection measures, spy on you, all before I would presentr myself to you and then I would ask you to get even better access to your environment.
Would you protect yourself up to applicable law, or would you accept it and put me in your friends and grant me better access to you? (And if you would just out desparation from longliness, would you do, even if you would be target of such approach daily, while occupied over your head with existing real relations?)
That is (from my point of view) exactly what are you asking about.
(If tracking would hit, than it would be when the email is opened, before adressee is able to read first line - and cannot find, if the email was actually read, most it can do is tell if it was opened. And it nearly make sure you will be ignored and emeail deleted without reading at the best, (if it is discovered), more probabelly resulting in some worse case, from automatic rejection, maybe blacklisting, maybe contacting your school/employer, up to some official actions))
Not that such approach would work against myself, as I have all emails sorted first to apropriate directories (Family, Friends, lists/ConferenceA, lists/ConferenceB, ... Partners/A, Partners/B,... reports/A, reports/B ... reports/unimportant/A,reports/unimportant/B, ... Spam ...) and what is left (not met by any crieria) in Inbox I consider possible spam more than anything else.
And I did set my email client to not automatically confirm delivery nor opening email. And to shouw only plain text (if email is only in HTML or other format, then it is presented as empty and usually deleted under assumption of being spam/malware/virus anyway without any attempt to see the content - except for a few manually explicitely named exceptions). And even if I open HTML attachement, it is not allowed to access internet (no images/css/flash ...) and of course all flash/(java)scripts/similar are baned from being run. And I would not run/install any program from email.
I reported back to authorities a lot of such emails as being unwanted and offensive. Some of such actions indirectly helped to the court and fine for the sender.
If you want to get positive answer from me, then I suggest (as other stated here) make your email as simple to deside on as possible.
- use short, but descriptive subject
- start with short (like one line/sentence/ short paragraph) summary in neutral tone ( I look for position as XXX, have this school/grade, I participated on YYY, more in email and on my website htpp://my.web.site/folder)
- then write the "full official" body with addressing/greating, describing why you are sending this (read about free position there, wanted to participate on this, interested on that field ...), what you archived yet (if you have something related) etc, etc - just the letter you wanted to send.
- if you send Curriculum Vitae, documents and such it is possible to include them as attachements, if they are short and important (and you can mention them in the email too)(longer document should be saved on web and provided by links to them - nobody wants have its email filled with multimegabytes messages from strangers), it is better, if the name is descriptive for the receiver (my_name_CV.doc, my_name_awards.html ...) then just common(CV.doc), as the professor probabelly have tons of CVs. Surely do not name it from your point of view (CV_for_proffesor_this_and_that.doc), even if you store it with such name on your comp (still is better to make directory on your computer named by this professor and store it there with your name on this, in case he/she would later ask you about 3. paragraf in my_name_CV.doc, then you can simply find, which CV it is and what exactly was there. The same, if you are later asked to resend that, maybe because it was accidentally deleted)
- end the letter with your full name, email address and any other contact informations you want to share (including the website about yourself) - it is better, if the message is printed, saved/resend, that all contacts to you are included (as email headers can be stripped, or your email would be resend many times and finding, who is the author is difficult/impossible)
All other rules of proper coresponding also applies, but you surely know that.