...in the URL field you would need to enter a 'mailto:' command:
mailto:someone@somebody.com
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...to add subject line automatically:
mailto:someone@somebody.com?subject=some custom text
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...to CC somebody automatically:
mailto:someone@somebody.com?cc=another@another.com
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...to blind copy somebody automatically:
mailto:someone@somebody.com?bcc=another@another.com
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...to add text to actual body message automatically:
mailto:someone@somebody.com?body=I am having trouble finding information on
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...to add multi line text to actual body message automatically:
mailto:someone@somebody.com?body=TYPE FIRST PARAGRAPH.%0A%0ATYPE SECOND PARAGRAPH.%0A%0ATYPE THIRD PARAGRAPH.
NOTE: Use "%0A" for a new line, use "%0A%0A" for a new line preceded by a blank line.
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...to use Subject, a Recipient, a Copy and a Blind Copy automatically:
mailto:someone@somebody.com?subject=some custom text&cc=another@another.com&bcc=jbloggs@jbloggs.com
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Andrew