Hi Laurence,
MailMerge v1.4 now supports multiple addresses in TO, CC, BCC recipient fields.
Separate addresses with pipe (|) or new-line (char:10 or Alt+Enter) characters.
Attachment filenames may also now be pipe or new-line separated.
In the latest version, if your email addresses are in separate columns (and you don't want to CC some and BCC others) you'll want to concatenate your addresses in the 'To' column of your spreadsheet separated by a pipe character (|) or line-feed character (Char(10) / Alt+Enter). Using a simple Excel formula to achieve this probably best.
E.g. Supposing your email addresses are in columns G and H of your worksheet, in the first cell of the column you've set with the 'To' header, you could enter formula =G2&" | "&H2 or =G2&Char(10)&H2 and fill down. This will insert both those recipient addresses into the 'To' field of the draft emails.