I have not tried this but under Squirrelmails addresses page is the import section. You browse for your CSV file and can select your options for the CSV file from drop down menus.
The max file size is 10KB (I suppose you could split the file if it were larger)
Input character set...all the usual ones.
Field delimiter: (can be) ' , " ; or a custom delimiter
Text delimiter: (can be) the same as for field delimiter
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I am NOT a DreamHost employee OK! :@
Act on my advice at your own risk!