The best way to write a regret letter for not participating in an event is to write and send the letter before the event takes place, as the person whose event you cannot attend will know this in advance. However, these types of letters can also be sent after the event has taken place.
After the obligatory "Dear Mr X" at the start of the letter, the very first sentence you should write should be an apology for being unable to attend the event. Make sure that your apology sounds sincere and heartfelt, and is very clear. A phrase such as "I am genuinely very sorry that I am unable to attend your event" is simple but effective.
An excuse would be something along the lines of "I'd like to come BUT I'm doing something else", and should be avoided. Excuses sound insincere and careless, which could just offend the host further. Instead, give a reason for your not attending, and make sure it's legitimate. A sentence such as "unfortunately I have a doctor's appointment at the time of our meeting" or "unfortunately I will be out of town on the weekend of your party" is acceptable.
Your letter should reassure the host of the event that you will not miss out on any further events - this occasion can therefore be seen as a one-off and will not damage your working, social or other type of relationship with the host. A phrase such as "if you should choose to invite me to your next party/meeting/event, I will not let you down again" is desirable.
Finish your letter with a further apology or expression of regret, such as "once again, I'm very sorry that I am unable to attend", followed by "yours sincerely" or another such sign off.
- Get straight to the point
After the obligatory "Dear Mr X" at the start of the letter, the very first sentence you should write should be an apology for being unable to attend the event. Make sure that your apology sounds sincere and heartfelt, and is very clear. A phrase such as "I am genuinely very sorry that I am unable to attend your event" is simple but effective.
- Give a reason for not attending - don't give an excuse
An excuse would be something along the lines of "I'd like to come BUT I'm doing something else", and should be avoided. Excuses sound insincere and careless, which could just offend the host further. Instead, give a reason for your not attending, and make sure it's legitimate. A sentence such as "unfortunately I have a doctor's appointment at the time of our meeting" or "unfortunately I will be out of town on the weekend of your party" is acceptable.
- Look to the future
Your letter should reassure the host of the event that you will not miss out on any further events - this occasion can therefore be seen as a one-off and will not damage your working, social or other type of relationship with the host. A phrase such as "if you should choose to invite me to your next party/meeting/event, I will not let you down again" is desirable.
- End with another apology
Finish your letter with a further apology or expression of regret, such as "once again, I'm very sorry that I am unable to attend", followed by "yours sincerely" or another such sign off.
