verbs - Which form is はじめまして?

So I've learned that はじめまして is used in first meetings and that it stems from the verb はじめる (to start; to begin). But what form is it? It's apparently not the polite past form, which has a -た at the end (はじめました). Is it a proper verb form of はじめる anyway or should it simply be seen as a set expression?

Answer

To break it down, はじめまして is the て form of はじめます, and はじめます is the polite form of はじめる.

はじめまして is a fixed expression.

You'll see ～～まして in some fixed expressions such as:

• あけましておめでとうございます。-- Happy new year.


• どういたしまして。-- You are welcome.

as well as in polite/formal speech or writing such as:

• ご来店くださいまして、誠にありがとうございます。
  
  -- Thank you for visiting our store.


• ご迷惑をおかけしまして、申し訳ございません。
  -- We are sorry to have troubled you.