Unable to send invitation

SInce my upgrade to version Version : 4.7.1 (4.7.2), I have some troubles with my configuration with the following message:
[EROR] Failed to send invite email successfully err=SendMail: Failed to authenticate on SMTP server, x509: certificate signed by unknown authority
I have checked the SMTP parameters and it seems OK; my certificate is a Let’s encrypt certificate

What’s wrong ?
Thanks for your tips

I have setup a new gmail account to be sure that it is not my mail server and I have this message:
[2018/03/28 23:18:35 CEST] [EROR] Failed to send invite email successfully err=SendMail: Failed to authenticate on SMTP server, 535 5.7.8 Username and Password not accepted. Learn more at
5.7.8 https://support.google.com/mail/?p=BadCredentials p19sm7676050wrb.75 - gsmtp

of course, I am sure of the user/password

Have you tried allowing less secure apps? https://support.google.com/accounts/answer/6010255

YES, it is good with gmail :slight_smile:
thanks