If debug shows the reset message was sent to the SMTP server successfully, then Moodle is done with it's part of an email. The message is now under control of the SMTP server ... it must be set to allow relay from your Moodle server to the address.
So, access the SMTP server and look at it's logs/configuration. SMTP servers typically have to be configured to allow the moodle server to relay mail through it.
IF the SMTP server is using blackhole checking or SPAM checks or it checks for SPF or DKIM records in DNS for your moodle server. Then you'll have to set up those DNS records. Contact whomever administers the SMTP server for assistance.
'spirit of sharing', Ken