When you try to send e-mail messages or to receive e-mail messages through Microsoft Entourage for Mac, you receive one of the following error messages:

• Error: Mail could not be sent using account account_name. An error of type -3155 has occurred.
• Error: Mail could not be received using account account_name. An error of type -3155 has occurred.

Additionally, you experience one or more of the following symptoms:

• Messages that have attachments that are larger than ordinary may cause the error. However, smaller attachments may be sent.
• Messages that have attachments remain in the Outbox.
• E-mail messages that have no attachments can be sent and received without any problem.
• Other error codes that might be reported are 111, 3259, and 5421.

You may experience these symptoms in Entourage for Mac or when you access Outlook Web Access by using any browser on the same Macintosh computer.

There are two main reasons for this set of symptoms to occur.

Cause 1

This problem may occur if your Internet service provider (ISP) has a maximum size limit for attachments, and the e-mail messages that you send or receive include attachments that are more than that limit. Typically, this problem occurs when programs or graphics are attached to your e-mail messages.

Cause 2

This problem may occur if the maximum transmission unit (MTU) size setting on the user's Macintosh computer is set to a low value. The MTU is sometimes increased to yield increased performance in DSL and cable modem environments.

Workaround for Cause 1

Sending messages that have large attachments

Use any one of the following techniques when you send e-mail messages that have large attachments:

• Use third-party programs to compress attachments to your e-mail messages.
• Try to adjust the scan or the graphic settings in your attachments so that the final size of your attachment is smaller. Typically, fewer colors produce a lower resolution and fewer pixels produce smaller files.
• Post pictures on a Web site instead of sending pictures as e-mail attachments. Then, send your intended recipients the link to that Web site.

Receiving messages that have large attachments

When you receive large e-mail messages that have large attachments, contact your ISP. Your ISP can help you remove these messages from your Inbox on your e-mail server. Additionally, contact e-mail senders, and then recommend that they use one or more of the techniques that are listed in the "Sending large messages" section.

Workaround for Cause 2

The most frequently recommended size setting for the MTU is 1492. To reset the MTU size to 1492, follow these steps:

1. On the Macintosh computer, click Hard Drive, click Applications, click Utilities, and then click Terminal.
2. Type the following string, and then press ENTER:
   sudo ifconfig en0 mtu 1492
3. Type the Administrator account password if you are prompted.
4. Quit Terminal. Then, try sending an e-mail message that has an attachment again in Entourage for Mac.

This change is reset when you restart the computer. Therefore, there is a script that you can configure to run at startup. The script automatically changes the MTU setting on every restart. We do not support the script. However, we provide a link to the script to help our customers. To see the script, visit the following Apple Web site:
http://docs.info.apple.com/article.html?artnum=107474 (http://docs.info.apple.com/article.html?artnum=107474)