authentication failure [SMTP: STARTTLS failed (code: 220, response: 2.0.0 Start TLS)]


I am getting the above error message when trying to setup my outbound email. I'm using mailgun and have the drupal smtp module setup and working using identical details.

Any ideas where to start troubleshooting this?


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1 Answer 1


This question appears to be the same as Outbound mail fails after upgrading to 4.7.1 tl/dr i suspect your probably running on php5.6 or similar version and the ssl certificate for smtp.mailgun.org is not valid or is a CACert or similar and PHP5.6 is saying i can't validate certificate.

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