SMTD-300 — Cannot read mail body line
Mail line is longer than allowed maximum or input buffer size. The description text specifies whether it was a regular body text line, body line encoded by base64/quoted-printable, or it was a SMTP/MIME header (multi)line.
In the case of buffer size limitation, you can increase buffer size setting (SMTP-PROXY.CLIENT-CONN.RECV-BUFSIZE, POP3-PROXY.SERVER-CONN.RECV-BUFSIZE etc.).
In the case of RFC limitation on mail/subdocument body text line, you can allow accepting such mails by specifying the SESSION-ACL.MAIL-LINE-LEN configuration directive.
In the case of encoded line, the RFC limit (76) can be increased by the MAIL-FILTER.ENC-LINE-LEN configuration item.
In the case of too long header line, the proxy behaves according to the MAIL-FILTER.LONG-HEADER item(s).
Further mail processing depends on error severity and proxy configuration, read next log messages.