How can I say "long time no see" on email?

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I would typically write something like...

Hey John,
Sorry I haven't written for a while. [ rest of your letter ]

or

Hi John,
I hope this letter finds you well. It's been a while. [ rest of your letter ]

or

Hi John,
Wow. It's been a while since we last communicated. I'll try to be better in the future.


Basically, I immediately spend a short sentence or two acknowledging that is has been some time since I last wrote, then I often offer a mild apology, and then then I get on with my letter.