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Wednesday, July 11, 2012, 17:23

Why do I get an "Invalid Source Address" error when e-mail addresses are separated by a semi-colon delimiter?

Category: Configuration

Solution ID: 00000153


Why do I get an "Invalid Source Address" error when e-mail addresses are separated by a semi-colon delimiter?


This error often occurs when custom scripts are created to send e-mail notifications, mail blasts, etc. The use of any separator character other than a comma ',' is not standards compliant. The Internet Message Format RFC 2822 requires lists of e-mail addresses to be separated by the comma ',' character. A semi-colon ';' is only allowed at the end of a group specification, not to speparate addresses.

This situation can occur when programmers use a semi-colon ';' delimiter to separate addresses in e-mail address lists when creating custom e-mail routines. The confusion can occur when programmers consistently work with and test on Microsoft mail products, or other products which allow a semi-colon ';' delimiter.

Programmers should write scripts/programs which are sandards-compliant to avoid mail delivery issues.


The Microsoft Mail (MSMail) product was introduced for PC networks in 1991. Microsoft Mail was a shared-file mail system using a database of shared files (via mapped network drives) as the "postoffice". The Microsoft Mail product used a semi-colon ';' to delimit address lists.

The Simple Mail Transport Protocol (SMTP) commonly used for tranferring messages via the Internet specifies the use of the comma ',' to delimit addresses, in an address list.

Microsoft has kept the use of the semi-colon ';' delimiter as a proprietary standard for messages "displayed" in their mail products. However, when sending e-mail through the Internet via SMTP Microsoft servers translate the semi-colon ';' character to a comma ',' to remain standards complient.


In short, regardless of how a message is displayed in an e-mail client, it must be transmitted using SMTP standards compliant formatting (i.e. RFC 2822). Specifically, e-mail address lists must be delimited using the comma ',' delimiter.

For more information refer to:

Tags: source address, error, semicolon, semi-colon, comma, delimiter, delimited, email, address, lists

See Also:

Link to this article: kb/invalid_source_address_semicolon

Updated: Wednesday, July 11, 2012, 17:23

-- David Rutherford


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Last modified: 2012-11-22, 11:01

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