UPDATE 1/30/2010: This issue has been resolved. Thanks for your patience!
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This morning, a few customers have reported they experienced difficulty sending individual (“one-off”) plain-text messages. You might recall, we had this problem and fixed it last week. Well, now it’s back.
We’re aware of the issue and are working to resolve it quickly. It has been elevated to a critical status and we’re looking into it now.
The workaround is to send the message as HTML format and it should work.
It is important to point out this does not impact broadcasts, follow-up sequences or other system-generated emails.
We’ll let you know when this is fully resolved.