server denied authentification

Hi, I've 4 server with plesk 18.0.31 #2 and from all server no client can send mail from webail and horde or roundcube. They have always the same error: "There was an error sending the message: Server denied authentication" From pc all work fine but with webmail is impossible to send email...

Hi, I've install postfix and dovecot, and if i try to reply or transfer mail from horde, i've this error : server denied authentification. This domain is on dedicated ip and have an ssl wildecard certificate. I've try to restart service and server : not change Can you help Me ?