Code Page Enhancements for CSSMTP

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The z/OS Communications Server SMTP (CSSMTP) client was introduced in z/OS V1R11 to provide a modern, RFC-compliant mail client that would perform better and provide superior client function to the existing SMTPD program. Unlike SMTPD, CSSMTP supports IPv6 and can have its communications with a mail server secured with application-transparent TLS (AT-TLS).

In February of 2014, IBM issued a statement of direction (SoD) that stated that support for SMTPD and sendmail would be removed in a future release. In July of 2015, a subsequent SoD further elaborated on that direction by stating that z/OS V2R2 would be the last release to include SMTPD and sendmail.

z/OS V2R3, which became generally available in September of 2017, fulfills that SoD by no longer including SMTPD or sendmail. With V2R3, CSSMTP is the only mail client provided with z/OS. (z/OS no longer provides a mail server capability in z/OS V2R3.)

There was one significant capability missing from CSSMTP as compared to SMTPD: support for multibyte character sets (MBCS). MBCS translation, and in particular, double-byte character set (DBCS) support, is a capability that was supported by SMTPD and is used by many customers in some geographies. As such, the lack of DBCS support in CSSMTP is a hindrance to CSSMTP acceptance in those geographies, and therefore an inhibitor to customer migrations to z/OS V2R3.

The good news is that this missing DBCS support is now being provided through new-function APAR PI93278 for z/OS V2R1, V2R2, and V2R3. Unlike SMTPD, which depended on translation tables, CSSMTP's DBCS support is enabled via specification of a multi-byte code page through a new MBCHARSET operand in the CSSMTP configuration file (along with an MBCS switch to control whether MBCS capability is to be enabled at all). A table in the IP Configuration Guide provides suggestions as to which code page to specify on the MBCHARSET parameter.

An Additional Enhancement for SBCS Users

APAR PI93278 is labeled "code page enhancements' because there are actually two significant enhancements provided via this APAR. In addition to MBCS support, the APAR also provides improved handling of single-byte character set (SBCS) special characters in the mail subject line. Previously, some special characters, such as the euro symbol (€), were not translated correctly. This APAR is also intended to address that issue.

PTF information
The PTFs for APAR PI93278 are:
V2R1: UI56996
V2R2: UI56997
V2R3: UI56998

For those exploiting the MBCS support, you should also apply the PTF for APAR OA55727 from Unicode Services:
V2R1: UA96702 
V2R2: UA96700
V2R3: UA96699