I send a short email also:
Dear ___,
This letter serves as notice of our intent to increase the monthly rent at _______. from $__ to $__ beginning _____.
After careful consideration, we’ve determined this increase is necessary due to our increased utility and maintenance costs. We are providing this notice well in advance to allow you ample time to plan for this change. You have been a great tenant, and we hope you will choose to continue the lease agreement under these new terms.
Please confirm your acceptance of these terms by responding to this email. If you reject the terms of this increase, your current lease will expire on _____.
Sincerely, ___
Don't overthink it or apologize or offer anything to "soften the blow." Your costs increase every year, tenants expect incremental increases in rent. I felt bad when I sent my first increase notice too, but you have to cover your costs to keep the homes up. It gets easier with experience.