SMTP mail will not work

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Nextcloud version 13.0.5.2
Operating system and version Ubuntu 16.04
Apache or nginx version 2.4.25
PHP version 7.0.31

I cannot define SMTP E-Mail
port 465 SSL/TLS or 587 STARTTLS
it will not work, only with PHPMAIL

repeating the following error
Error PHP is_readable(): open_basedir restriction in effect. File(/proc/meminfo) is not within the allowed path(s): (/var/www/vhosts/domain.tld/:/tmp/:{/proc/meminfo}:/dev/urandom) at /var/www/vhosts/overalldomain.tld/sub.domain.tld/apps/serverinfo/lib/SystemStatistics.php#74

The output of your config.php file

  'instanceid' => '',
  'passwordsalt' => '',
  'secret' => '',
  'trusted_domains' => 
  array (
    0 => 'sub.domain.tld',
  ),
  'datadirectory' => '/var/www/vhosts/overalldomain.tld/sub.domain.tld/data',
  'overwrite.cli.url' => 'https://sub.domain.tls',
  'overwriteprotocol' => 'https',
  'dbtype' => 'mysql',
  'version' => '13.0.5.2',
  'dbname' => 'adminn_db',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'dmin_db',
  'dbpassword' => 'abcdefghij',
  'installed' => true,
  'mail_smtpmode' => 'smtp',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpsecure' => 'ssl',
  'mail_from_address' => 'mail',
  'mail_domain' => 'domain.tld',
  'mail_smtphost' => 'mail.domain.tld',
  'mail_smtpport' => '465',
  'mail_smtpauth' => 1,
  'mail_smtpname' => 'mail@domain.tld',
  'mail_smtppassword' => 'password',

when I put the data in thunderbird in and outgoing mail is working.

So do you have /proc/meminfo in your open_basedir?

Thanks for your response.

Yes I have this in my PHP settings in Plesk
{WEBSPACEROOT}{/}{:}{TMP}{/}{:}/proc/meminfo{:}/dev/urandom

I get the following notification

(Error: Connection could not be established with host mail.domain.tld [ #0])

Regards,
Jan

Not sure your Plesk setup has the correct syntax. Obviously it is not recognized.