When to use ‘To whom it may concern’ versus ‘Dear Sir or Madam’

It is a common question that many turn to Google to answer. Whether you are writing a professional letter to an institution or an established individual, when is it appropriate to open with ‘To whom it may concern’ versus ‘Dear Sir or Madam’? Truthfully, the answer isn’t exactly black and white.
Generally, ‘To whom it may concern’ should be used when writing to, or written by, someone without regard as to the recipient, whether it be a company, institution, or person. Additionally, it is best when the recipient is a third party to the matter at hand and if you do not know who’s hands it will come to.
‘Dear Sir or Madam’ should be used when the letter is a bit more specific, such as when the individual has a direct involvement in the matter at hand. This opener also is best suited when writing to someone specifically, whose identity you know, but are unable to obtain the name of.
The former opener is considered more impersonal while the latter is considered more personal and still polite. However, it is always best to try to find out the name of the person you are seeking to address, if applicable. It is understood that sometimes that is not possible. It is also important to consider that both of these forms of address are considered dated to some and that it may be worth finding an alternative. Both ‘Dear [the individual’s job title]’ or ‘Greetings:’ would be acceptable in these cases.