It is possible to remove the word ONLYOFFICE at the beginning of the notifications as shown in the following images:
Unfortunately, it’s impossible to customize the subject of the letter.
Thank you @Kate for your answer, but in the subject it is only appearing in the notifications of forgetting your password and email activation in the others it does not appear at the beginning of ONLYOFFICE, can it be considered for future corrections?
@NathalySuarez_25 Thank you for the clarification. I will forward this request to the responsible specialist.