Fix for the messaging interface has returned an unknown error
PST files are meant for saving large amount of data securely which is accessible with outlook. But, the problem that comes in the way is issues with outlook that arises out of result of large size of PST file. It is as such since; files of large size are more susceptible to corruption owing to file size limitation.
Excessive increase in PST file size, leads to abnormal termination or non responding Outlook and this can be experienced any time while carrying typical task, downloading or sending emails, accessing calendar records or contacts etc. To overcome file size limitation found, outlook 2003 uses new data structures. In spite of this, issues regarding performance and operation are not fully resolved.
As for instance, error message as “the messaging interface has returned an unknown error. If the problem persists, start outlook again” may be received while usual processes going on with outlook.
Frequency of appearance of “unknown error in messaging interface” is slightly increased at times checking mail, creation or deletion of calendar or inbox items, contact etc. resulting in failure of critical operations.
Since the problem takes place due to large PST or reaching inbuilt file size limit, PST splitter is required to sort it out.
Some of the steps you may try to fix messaging interface unknown error
- With the help of ‘allow upgrade to large tables’ feature included in Microsoft Outlook, limit of messages a folder is supposed to contain can be increased. Likewise, PST file folders can be increased.
- Reducing PST file size by removing items from deleted items folder
- Creating new PST file and PST contents imported to it
However, if you do not get required results or the process fails use PST splitter to break large PST into small based on date, time, folder or email-ID. Since it is compatible with outlook 2000, 2002, 2003, 2007 etc, so messaging interface unknown error taking place with any of them can be resolved.

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