You should definitely consult with an intellectual property attorney in NYC.
Generally speaking, there are three areas of intellectual property law; trademarks, copyrights, and patents. Macy's has a trademark (legal right) on their name and many things associated with it. You have a copyright in the photographs you took.
The domain name is a dicey area; it's my initial impression that Macy's may just have done a fishing expedition, sending out letters like the one you received to many sites that contain the name 'Macys' in the URL.
It is my initial impression that so long as you aren't creating a website that holds yourself out to confusion that you are, or are part of / affiliated with Macy's, then you will be secure in your rights to the website.
I checked, and it definitely just links to your personal photography website. No confusion or representation that you're Macy's, that's for sure.
However, I will defer to the IP attorneys to talk this up further. Best of luck.
No attorney will, or should, offer you specific legal advice via this forum. What you get is general legal information, the controlling law, and thoughts about how to think through a legal issue. And sometimes various practical options on how to proceed.
In your case you need to deal with the fact that Macy's owns the federally registered trademark "Macy's Thanksgiving Day Parade" [see http://tarr.uspto.gov/servlet/tarr?regser=serial&entry=75343573 ].
You also need to deal with the fact that the Macy's parade is an enormous advertising event for the company -- and so it is quite reasonable for consumers to believe that photosofmacysthanksgivingdayparade.com is a domain name and website either owned and operated by, or sponsored or endorsed by, Macy's.
Moreover, even if Macy's doesn't sell photographs of its parade, the law provides that "[a] person shall be liable in a civil action by the owner of a mark ... if, without regard to the goods or services of the parties, that person ... has a bad faith intent to profit from that mark ... and ... uses a domain name that ... is identical or confusingly similar to that mark."
All in all, my sense is that you may not have the better of this argument. But only your own attorney can assess the situation after reviewing all the facts. Good luck.
The above is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
Macy's is very aggressive in enforcing its trademark rights and copyright rights. Although you own the copyrights in the photographs that you took, the domain name that you purchased probably infringes Macy's trademark rights---they certainly will believe that is so. Further, to the extent your photographs contain trademarks and/or including copyrighted characters, your photographs might be deemed to violate trademark and/or copyrights. For example, if your photographs contain pictures of cartoon balloons, you may have violated rights of several parties, including the trademarks shown in the balloon floats (Macy's and others), the copyright in the cartoon character, and the copyright (probably owned by Macy's) in the design of the float. In short, you might need a license from several people to sell or display these photographs. Here is your problem---you are trying to benefit commercially by associating yourself with a famous event and the characters that participate in it. Any time you try to benefit commercially by such an association, you risk violating IP laws if you do not have permission to do so from the owners of applicable IP rights.
This situation is not going away. Macy's could decide to sue you (which would be very expensive) if you do not take prompt steps to settle this matter. You need (rather urgently) to retain intellectual property counsel to deal with this situation. And yes---this is going to cost you some money to resolve. If you force Macy's to sue, the defense costs will be tens of thousands of dollars. It will be far more cost effective for you to retain counsel to negotiate a settlement. And the longer you wait, the more costly this will be for you. You made a big mistake here---you tried to profit by associating yourself with the famous Macy's parade without having permission to do so. You need a lawyer to untangle this mess for you.