This was a wonderful surprise. The Wessexs very rare reply. It seems like their office just picks out a few letters & cards for each occasion to reply to. So, I was not expecting anything. This is my 3rd reply from the couple.
The front of the envelope looks very different than most of the replies you see from the UK Royals. The main reason is the Wessexs's mail isn't processed through the Court Post Office at Buckingham Palace. So, their mail doesn't feature that postmark. (For more on the Court Post Office, and different UK postmarks.)
Unlike other UK Royals, The Wessexs's mail isn't sent to their office in London. Instead, letters to the couple should be addressed to their home, Bagshot Park, where they have staff there to answer them.
This postmark has been used in the past for various royal residences, which is why it is not specific to Bagshot Park.
What is interesting is the postmark still feature's the old royal PPI (Printed Postal Impression) number W7047. The Royals changed the number in March to W4047, which is why they redesigned a number of their postmarks, including the one for the Court Post Office at Buckingham Palace. I expect they will update this postmark eventually. But, it's understandable that they would be a few months behind.
The back of the envelope features Prince Edward & Countess Sophie's joint coat of arm, along with the name of their residence, Bagshot Park. This envelope is used for both joint things from the couple, and solo letter sent on behalf of one of them.
In the envelope is a simple letter written by Jackie Phipps, their Secretarial Assistant.
The letter reads:
Bagshot Park05 July 2019
Dear Miss Daly
The Earl and Countess of Wessex thought it very kind of you to write to them on the occasion of their 20th wedding anniversary.
Although unable to reply personally, Their Royal Highnesses send you their best wishes,
Jackie PhippsHousehold of TRH the Earl and Countess of Wessex
The bottom of the letter features the address for Bagshot Park, which is what you want to use if you write to them. There is also a telephone and fax number.