how to change subject of activation mail

problem is that because of long subject my mail goes to spam box, and many user didn’t confirm their mail. Please tell me the solution as soon as possible.
Thanks in advance to help me

Hi,
There is an article if you want to change the subject of the e-mail: https://aaronjerad.com/blog/change-default-wordpress-account-activation-email-subject-message-sender/
If your e-mails goes to the spam folder there is a problem with your hosting server. You should contact them for help. Also you can use postmark or mandrill to make sure your e-mails are sent correctly.

Best regards,