MODAL VERBS: MAY vs CAN

Here are the simple rules:

Can is for ability:
"Can you drive a car with a standard shift?"
May is for permission or possibility: 
"You may borrow my car next week." (Permission)
"I may arrive late." (Possibility)

- See more at: http://www.businesswritingblog.com/business_writing/2006/08/can_vs_maynot_s.html#sthash.q4VivKBt.dpuf

Here are the simple rules:

Can is for ability:
"Can you drive a car with a standard shift?"
May is for permission or possibility: 
"You may borrow my car next week." (Permission)
"I may arrive late." (Possibility)

- See more at: http://www.businesswritingblog.com/business_writing/2006/08/can_vs_maynot_s.html#sthash.q4VivKBt.dpuf

Here are the simple rules:

Can is for ability:
"Can you drive a car with a standard shift?"

May is for permission or possibility: 
"You may borrow my car next week." (Permission)
"I may arrive late." (Possibility) 

But using the simple rules above, the choice between can and may may not be obvious in the sentences below. Which word would you choose?

1. Can/May I have food served in the conference room?
2. Yes, you can/may make arrangements with the onsite cafe.
3. Professional guests can/may have their parking tickets validated.
4. Please leave your phone number so that I can/may call you back.
5. Please approve these specifications so we can/may process your order.
6. You can/may review 440 lessons in the archives.

For the sentences above, does the meaning involve ability, possibility, or permission?

I would say each one involves ability. For example:

1. Am I able to have food served in the conference room?
2. Yes, you are able to make arrangements with the onsite cafe.
3. Professional guests are able to have their parking tickets validated.

I do not see the sentences as communicating permission, but another person might view them that way:

1. Am I permitted to have food served in the conference room?
2. Yes, you are permitted to make arrangements with the onsite cafe.
3. Professional guests are permitted to have their parking tickets validated.

My objection to may is that it may (possibility) be misunderstood. Do the sentences below indicate possibility or permission?

Professional guests may have their parking tickets validated.

Repeat visitors may receive a special discount.

I advise to follow this approach: 

If you intend "able to," use can.
If you mean "will possibly," use may.
If you intend "permitted to," use may. 

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Here are the simple rules:

Can is for ability:
"Can you drive a car with a standard shift?"
May is for permission or possibility: 
"You may borrow my car next week." (Permission)
"I may arrive late." (Possibility)

- See more at: http://www.businesswritingblog.com/business_writing/2006/08/can_vs_maynot_s.html#sthash.q4VivKBt.dpuf

Here are the simple rules:

Can is for ability:
"Can you drive a car with a standard shift?"
May is for permission or possibility: 
"You may borrow my car next week." (Permission)
"I may arrive late." (Possibility)

- See more at: http://www.businesswritingblog.com/business_writing/2006/08/can_vs_maynot_s.html#sthash.q4VivKBt.dpuf