[imp] Set default identity

[F Ringuello]

Dear all, I have horde 5.0.4 installed and all works fine, but now I have
to open several e-mail accounts for my new users and set the defaut
identity (name and address) for each of them, in order to send messages.
I know that each user can do that, but I need to set the identity for them.
I'm using mysql as backend.
For my existing users, I found, in the horde_prefs table, a row for each of
them with default identity, so I thought to create a standard user and copy
the row to new users, but I found a difference in the string from one user
to another i.e.:

For user joe:
a:1:{i:0;a:16:{s:16:"default_identity";i:0;s:9:"from_addr";s:13:"
joe at myaddress.com";s:8:"fullname";s:23:"My Name is Joe";s:2:"id";s:20....
and so on.

For user Jack:
a:1:{i:0;a:16:{s:16:"default_identity";i:0;s:9:"from_addr";s:26:"
jack at myaddress.com";s:8:"fullname";s:23:"My Name is Jack";s:2:"id";s:20....
and so on

The only difference is the address field that, for each user, have a
different prefix (s:13, s:26, etc.)

Someone can explain me the meaning of that "s:13 s:26 etc."?
How can I copy from one user to another if this field vary for all of my
existing users? What I have to write in this field?

Searching on horde wiki and on the web, I found some tips on how to use
hooks to get field from ldap to set default preferences, but my backend is
mysql and I want to write directly in db.


I hope to explain correctly my problem.
Thanks in advance for your help.

Regards
Franz