Postmaster Information

This e-mail service will do the following verifications for incomming e-mails:

  • DNS RBLs
  • virus scanning
  • RFC compatibilities
  • valid reverse DNS lookup
  • recommendations of the MAAWG
  • verify of SPF DNS records and DKIM signatures
  • for some remote e-mail services TLS is mandatory
  • different plausibility checks for HELO, RCPT TO, MAIL FROM
  • rejected MIME types are: application/x-msdownload, application/x-msdos-program, application/hta
  • relaying is only allowed using SMTP authentication in combination with transport layer security (TLS)
  • rejected file types are: .exe, .vbs, .pif, .scr, .bat, .cmd, .com, .cpl, .dll, .zip, .js, all Microsoft Office documents

For RFC 2142 role based mailboxes this policies vary.

Incomming connections can verify the issued TLS cerficate by DNS-based Authentication of Named Entities (DANE).

All outgoing e-mails of this e-mail service:

  • will prefer transport layer security (TLS) based on Perfect Forward Secrecy (PFS), for some remote e-mail services TLS is mandatory
  • will use DNS-based Authentication of Named Entities (DANE) for TLS certificate verification of the remote e-mail service
  • contain a valid DKIM signature
  • have a valid SPF DNS record
  • are virus scanned

Common error messages / häufige Fehlermeldungen:

  • 554 5.1.8 : Sender address rejected: Domain not found
    EN: Your sending domain used is not resolvable by DNS.
    DE: Ihre Absenderdomäne kann per DNS nicht aufgelöst werden.
  • 554 5.7.0 Reject, id=XXXXX-XX – INFECTED
    EN: A virus was found in your e-mail. Please verify your e-mail against an antivirus scan engine (e.g. VirusTotal).
    DE: In Ihrer E-Mail wurde ein Virus festgestellt. Bitte überprüfen Sie Ihre E-Mail mit einem aktuellen Antivirus-Programm (z.B. VirusTotal).
  • 554 5.7.0 Reject, id=XXXXX-XX – BANNED
    EN: For security reasons (e.g. malware) the attachment file type has been rejected. Please use a document format with limited active content (e.g. plain Portable Document Format (PDF)). Renaming or archiving of the attachement is not a given solution.
    DE: Aus Sicherheitsgründen (z.B. aufgrund von Malware) wurde der Dateityp Ihres E-Mail Anhanges abgelehnt. Bitte verwenden Sie einen Dateityp, der keine Makros o.ä. enthält (z.B. ein einfaches Portable Document Format (PDF)). Auch umbenannte oder gepackte Dateitypen werden erkannt und entsprechend abgelehnt.
  • 554 5.7.0 Reject, id=XXXXX-XX – spam
    EN: Your e-mail was classified as spam.
    DE: Ihre E-Mail wurde als Spam eingestuft.
  • 554 5.7.1 Client host rejected: Access denied.
    EN: Your client host is not allowed to send any e-mail directly to our mail services (e.g. dynamic IP address or listed in a DNS RBL) or has a missing DNS configuration (e.g. invalid or missing DNS PTR). Please verify your DNS configuration and try again later.
    DE: Der IP-Adresse des von Ihnen verwendeten Servers ist es nicht gestattet, eine E-Mail direkt an uns auszuliefern. Evtl. handelt es sich um eine dynamische IP-Addresse oder die IP-Adresse ist in einer Negativliste eingetragen oder die DNS-Konfiguration für diese IP-Adresse ist fehlerhaft bzw. nicht vorhanden. Bitte überprüfen Sie die DNS-Konfiguration und senden Sie die E-Mail erneut.
  • 554 5.7.1 Service unavailable; Client host [XX.XX.XX.XX] blocked using …
    EN: Your client sending this email is blocked by a blacklist.
    DE: Ihr Absendender Client steht auf einer Blackliste
  • 554 5.7.1 : Helo command rejected: Host not found;
    EN: Your send helo/ehlo command is not resolvable by DNS.
    DE: Ihr beim Versand verwendeter helo/ehlo Name kann per DNS nicht aufgelöst werden

Used DNS Blacklists / Verwende DNS Blacklisten

For Postscreen:


Configuration of end user e-mail clients

The following auto configuration mechanisms will be supported for end user e-mail clients:

For a manual configuration of end user e-mail clients the following settings are required:

STARTTLS Port 143 587 N/A
SSL/TLS Port 993 465 4190
Username username@domain.tld username@domain.tld username@domain.tld
Authentication method Regular password (PLAIN) Regular password (PLAIN) Regular password (PLAIN)


Please do not use IP addresses! Please use this hostnames only. SNI is not supported.

The Webmail Interface is available at

Contact / Kontakt

You can contact the postmaster by:

  • e-mail: postmaster [at] cscholz DOT io

Plesse provide the following information:

  • e-mail address of sender and recipient (mandatory)
  • date and time (mandatory)
  • error message of your e-mail service (mandatory)
  • log extract (highly recommended)
  • your phone number (opional)