When should someone put education credentials after their names? BS, MBA, MFA, JD, PhD etc etc etc when is it acceptable and at what level?

I think Masters and above.

Great question.
I hesitate to add to all the great answers already listed, but in my humble opinion, education credentials are appropriate when used in address to positions which require the credentials. For instance, when I go to the doctors' office, I would like to see my doctor with the title M.D. after their name in either posted or written correspondence; however, when I am corresponding with that same person outside of the medical complex I do not expect to see those credentials listed.

Typically in higher education the terminal degree is listed (PhD, EdD, DMin, MFA, etc.). A secondary degree may be listed if it is not trumped by the progressive terminal degree. For instance, a Dmin would not also include a MDiv, but a PhD may also list an MBA if in a different context and is working in both domains.

Thanks,
Brian

I believe that "Esquire" would be appropriate, however, anything else should be placed in a resume under the education section.

It should be noted that any time you are communicating in your military capacity you should use your rank and NO post-nominals. No sort of post-nominal abbreviation ... professional, academic, religious .. is ever used with a rank. Example of a CPT in the Army: Captain John Smith, USA. Even if he has a doctorate, you leave it out if rank is being used.

HOWEVER, if you are retired working in a civilian job, then you should use the form that supports that job and should not be using military rank and retired – it is a misrepresentation. You are an employee of the new employer and representing the new employer in your new official position – not the military. Those present because they are on active duty are Rank (Name); Those present, because they are working in a civilian role, are Mr./Ms. (Name). In this case you should not use your military rank and instead use the most applicable post-nominal to your specific job. In a social situation you can use your retired rank. Note that rank comes before the name, so as a retiree yours should be SGT Lawrence Prentice, USA, Ret. Also, (RET) is an incorrect usage, it's either USA, Retired, or USA, Ret.

Also, email signature blocks are different from written ones. Here is the proper formula for a DoD email signature block:
1) The NAME IS CAPITALIZED, followed by rank, then service on the first line.
2) The duty title is on the second line.
3) Other information such as in address, phone, cell, classified e-mail address, etc. Many people include a full mailing address as that would typically appear on official letterhead.
So a formula would be:
NAME, Rank, Branch of Service
Duty line / Name of office
Mailing Address
Phone Number(s)
Which look like this:
DEBORAH LASSITER, Lt Col, USAF
Title of Position
Name of Office
Pentagon, Room, Washington, D.C. Zip Code
Phone: [login to see]
Cell: [login to see]
or
TIMOTHY W. THOMPSON, LTC, USA
Title of Position
Name of Office
Address, Washington, D.C. Zip Code
Phone: [login to see]
So based on that a retired address block might look like:
DANIEL C. WALLACE, MSgt. USAF, Ret.
Mailing Address
Phone: [login to see]
But once again you wouldn't use this form of address block for a civilian job.

I got all of this info from http://www.formsofaddress.info/post_nominals.html#174 and there's a ton more on there for anyone interested. It's actually a very very complicated question when you dig way into it.

In addition to Kevin's sentiments, you'll find cultural norms often vary from one industry to the next. For instance, in many sectors, putting "MBA" in your signature block is frowned upon and thought of as self-aggrandizing. In other sectors, being able to legitimately put "MBA" in your signature block is the most valuable thing about going to business school in the first place. Situation dictates. When I worked in the intelligence and special operations community, there's no way I would have put MBA in my signature block - perhaps because it would have been viewed as irrelevant and self-indulgent. However, as a business consultant, I am often given credibility arguably before I yet deserve because the degree is in the sig block.