I was looking for the proper salutation and closing for Dutch communications and found a very useful page. The original can be found here:
http://www.dutchgrammar.com/forum/viewtopic.php?t=153
but I have extracted what I think are the best bits and have copied them below for posterity:


Some hello - goodbye expressions in no particular order:
Doei - bye-bye, cheers
Welterusten - good nite, nighty-night, sleep well
Trusten - same as above. I often see this abbreviation in chat rooms.
Tot straks - so long, see you later
Tot volgende week - till next week
Tot de volgende keer - till next time
Toedeloe - toodle-oo
Toedels - same as above, another chat room thing, but sometimes my teachers say it too at the end of class.
Vaarwel - goodbye, farewell
Adieu - goodbye
Tot ziens - see you, goodbye
Slaap lekker - sleep well
Hallo - hello
Hoi - hello, hi, howdy
Goedendag, goeiendag - good day
Goedemorgen - good morning
Goedenacht - good night
Goedemiddag - good afternoon


please:
polite / formal: alstublieft (formed from 'als het u blieft')
informal: alsjeblieft (formed from 'als het jou blieft')

thank you:
polite / formal: dank u (wel)
informal: dank je (wel) (I always write 'dankjewel' as one piece, I don't know if that's correct, actually! :oops: )

you're welcome:
graag gedaan!
geen dank!

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In a formal letter (e.g. a business letter or a letter to a person you don't know [well]) there's in fact only one salutation possible, which is Geachte heer of Geachte mevrouw followed by the person's surname only (i.e. no first names or letters) and followed by a comma. Titles are no longer usual either. After an extra space between the lines the text of the actual letter should start with a capital. If you don't know the name of the person you're writing to you can use Geachte mevrouw, mijnheer,. I prefer to put mevrouw in the first place, as (despite all wanted social equality between men and women) usually a lady will be the first one to read a letter in an office.

Examples:

Geachte heer De Wit, (note the two capitals)
Geachte mevrouw Johansen,
Geachte heer, mevrouw,
Geachte bewoners, (e.g. when writing to residents of a certain building or part of town).

The use of capitals in names containing words like van or de and the like is different in the Netherlands and Belgium. In the Netherlands those words do not have a capital if the first name or first letters are mentioned. Only if they are the first word of the name without anything before it (such as in the start of a letter) the first word of the name will have a capital letter. In Belgium the first letter of a surname will always have a capital, no matter if there's a first name or letters before it.

So when witing a letter to Peter van der Horst in the address you should mention De heer P. van der Horst and ifor salutation in the letter Geachte heer Van der Horst, but in Belgium the same Peter would be called Peter Van der Horst. The start of a Belgian letter will be the same as in the Netherlands.

For informal letters we have many more possibilities and they usually only contain first names:

Beste Peter,
Beste collega's, (Dear colleagues,)
Lieve Laura,
Lieve oom Peter, (Dear uncle Peter,)
Liefste (may be followed by a name), (Dearest ...)
Hallo John,
Hoi John,

etcetera. Lieve is especially for those with whom you have a really close relationship, be it erotical or not.


Closings
Formal letters:
Hoogachtend, (note the comma - Yours sincerely, Yours faithfully), and a little less formal
Met vriendelijke groeten, or
Met vriendelijke groet, (With kind regards).

In really informal situations (the people you address by their first names)there are many more possibilities again, which may vary according to the situation. Your imagination won't fool you. Some examples:

Met vriendelijke groeten, (too!)
Met hartelijke groeten, (With kind(est) regards; Best regards)
Groeten, (Greetings)
Groetjes, (Warm greetings)
Saluut, (See you!)
Tot ziens, (See you later)
Tot morgen, (See you tomorrow)
Tot volgende week, (See you next week, ... or whenever)

Liefs, (Love)
Kusjes, (Lots of love (and kisses))

Sterkte, (Take care, Take heart)
Hou je taai, (Take care of yourself, Never say die)

Nice for me as a Dutchman to learn some phrases in English.

Some remarks:
Toedeloe, toedels and adieu are old fashioned. saluut is Belgian (Flemish), not Dutch.

When in Amsterdam use the Amsterdam/Jewish slang word MAZZEL, pronounced with S though (Amsterdam people can't/don't pronounce Z) or LATER (meaning the same as the English word) when saying goodbye.

Note that the Dutch are often way more informal than British or Americans. So you can safely use dankjewel instead of dankuwel in 99% of the times.

I've heard "Doei" responded to with a shortened "Do" although it seemed to be a girl thing. But I could be wrong. Would one guy say Doei or Do to another guy without eyebrows being raised?

I think there is a form doeg, a mix of doei and dag?

There are three options and both men and women can use these:
doei
doei, doei
doeg

Doei - may be more of an Amsterdammer thing. I've heard a couple of my cousins outside of Amsterdam complain about it's use in the past. Though last spring I heard their kids using it.

...

Also "Tot zo" ( or is it "Tot so") for "see you soon." As in sooner than Tot ziens

Every country has their language purists, and so has Holland.
"Doei" is one of those words that is on the borderline of being acceptable to some and annoying to others, to the point that it makes them cringe. Maybe a bit like "Wazzup?" in English ;-)

If you'd put it on a scale from formal/acceptable to informal/annoying it would probable be like this:
Goedendag - goeiedag - dag - doeg - doei - doei doei

Still, lots of people say doei, not just in Amsterdam. I hear it mostly in the west of the country though (de Randstad). I'd say give it another 10 years and nobody will think twice about it...

In the east, close to Germany, you would hear a lot of people say "aju", "ajuus" or "tsjuus" (from the german Tschüss, and the first two a mixup with the french adieu).

Down south, in Brabant, everyone says Houdoe (pronounced as How Do in English, although it has different origins).

Re: doei/doeg/etc...

I recently stumbled on this article about the different variants of spoken (informal) goodbye expressions
used in the dutch language. It is written by a sociolinguist based on polls.
Although the article is in dutch, you may find the second map (afscheidsgroet 2008) interesting.

http://www.janstroop.nl/artikelen/Groetenenwensen.shtml

It confirms several of slick's observations.

Slick wrote:
> I'd say give it another 10 years and nobody will think twice about it...

Probably you are right. The writer noticed the spreading of doei/doeg throughout the whole Netherlands with
doei being the most used.

Boobmanz wrote:
> saluut is Belgian (Flemish), not Dutch.

It is dutch. Just a form not or rarely used in the Netherlands, except as a military greet.