Send mail error when approving users

I am using an old version of tml and am having a send mail error show each time an admin tries to approve the users ‘The e-mail could not be sent.
Possible reason: your host may have disabled the mail() function…’ however I have told the wordpress to send email by smtp using the ‘WP Mail SMTP’ plugin but no luck, I am able to send the test fine and tried disabling all other plugins but no luck