Arcules users need an email address and a mobile phone number to register. Arcules requires unique email addresses but allows the reuse of phone numbers.
An efficient method is to use plus sign email addressing and the mobile phone of a technician.
To use plus sign email addressing (https://datatracker.ietf.org/doc/html/rfc5233), append a + sign and desired descriptor after your account name and before the @ symbol (e.g., jane.doe+customtag@arcules.com). This allows many unique email address aliases to be delivered to a single email address.
Many email services support RFC5233 / plus sign email addressing / subaddress extension, but notably Office 365 does not.
Update the service user account with the corresponding unique email address using plus sign email addressing or another preferred method (https://arc-cs-01.arcules.com/en/articles/2035624-people) and reinvite/resend invite email the user. Enter the technician's mobile phone for the service account and register. The service account will then be active and can be used.