This article describes how to include multiple email addresses in the To: header field, or how to add additional recipients via the Cc: or Bcc: fields. When inserting multiple email addresses into any of these header fields, ensure that they are properly separated.
Separate with a Comma
Most — but not all — email clients require that multiple email addresses be separated by a comma in any of their header fields. The correct way to separate email addresses in the header fields of these email providers is as follows:
and so forth. Commas are the preferred method of punctuation in nine out of ten email programs. They work perfectly well, unless you are using Microsoft Outlook. Certain email clients, such as Gmail for Android, accept either a comma or a semicolon as the separator.
An Exception to the Rule
Outlook and any other email program that searches for names in the last name, first name format and uses the comma as a delimiter may encounter issues if you use commas to separate email recipients. To separate multiple addresses in their header fields, email clients that use commas as delimiters typically use semicolons. Multiple addresses are entered in Outlook by default using semicolon separators.
You should be fine if you switch to using the semicolon as a separator in Outlook. If you have difficulty adjusting to the change or frequently forget and receive the name could not be resolved error message, you can permanently change the Outlook separator to a comma.
Change the separator in Outlook to a comma
In Outlook 2010, you can change the preferences to use a comma rather than a semicolon in the headers by going to File > Options > Mail. Select the checkbox next to Commas. This can be used to separate multiple message recipients in the Send messages section, and then click OK at the bottom.
Navigate to Tools > Options > Preferences in Outlook 2007 and earlier. Select E-mail Options > Advanced E-mail Options and check the Allow comma as address separator check box. To save and return to Outlook, click OK on any open windows.