Note that
https://github.com/go-gomail/gomail is apparently no longer maintained (the last commit was seven years ago). And
https://github.com/go-mail/mail claims to be an actively maintained fork of the previous project but the most recent commit was four years ago. It's possible the project is stable and (mostly) bug free but that seems unlikely given the open issues:
https://github.com/go-mail/mail/issues/. It also states that it requires Go v1.2 or newer; which is an ancient version of Go (another red flag the project should probably not be used). If you're using some other version of "GoMail" it would help if you provided a link to the project.