Outlook o ThunderBird

no está configurado correctamente en las opciones avanzadas, en la seccion opciones internacionales. Si el error se presenta intente configurar las opciones de esta manera:



En la casilla "Seleccionar la codificacion" escoja UNICODE UTF-8
En la casilla "Seleccionar codificacion vCards " escoja UNICODE UTF-8


PARA THUNDERBIRD



O puede leer un articulo mas completo:

Setting Outlook to Use UTF-8

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Many of the fonts included with Microsoft Windows have support for languages with non-Latin characters such as Hebrew, Greek and Arabic. However, you must configure Outlook 2010 to use Unicode UTF-8 text encoding to combine non-Latin characters with English characters in email messages. Enabling UTF-8 encoding in Outlook also allows you to use non-Latin characters when typing email addresses. Enable these options in the Advanced section of the Outlook Options menu.
Step 1Click the orange "File" tab in the top left corner of the Outlook 2010 window and click "Options" on the pull-down menu. A new window titled "Outlook Options" appears.

Step 2Click the "Advanced" heading on the left side of the window and then scroll to the "International Options" heading near the bottom.

Step 3Place a check in the box labeled "Automatically select encoding for outgoing messages" and click "Unicode (UTF-8)" on the drop-down menu.

Step 4Place a check in the box labeled "Automatically select encoding for outgoing vCards" and click "Unicode (UTF-8)" on the drop-down menu.

Step 5Place a check in the box labeled "Allow UTF-8 support for the mailto: protocol."

Step 6Click "OK."