Unable to send welcome emails to defined users

I'm using profiller to define several default user accounts like so:

users[superduper][uid]    = 1
users[superduper][name]   = admin
users[superduper][mail]   = admin@example.com
users[superduper][roles]  = administrator
users[superduper][status] = 1

users[manager][uid]       = 2
users[manager][name]      = manager.test
users[manager][mail]      = manager.test@example.com
users[manager][roles]     = manager
users[manager][status]    = 1

users[editor][uid]        = 3
users[editor][name]       = editor.test
users[editor][mail]       = editor.test@example.com
users[editor][roles]      = manager
users[editor][status]     = 1

As far as I can tell, the user accounts are crated correctly. However, no welsome email are sent and there are errors reported stating "Error sending e-mail (from tom@example.com to ). So the to address for these users is blank for some reason when drupal tries to send the emails - even though they have been defined in the .info file.

This stops installation from completing when run from Aegir, as these are reported as errors.