Strange case - digital signature w/o encryption does not work?

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1

Hi,

Recently I applied for your free email certificates for private email account.

Everything was installed without any problem.

Now, I wanted to enable encrypted communication with my company email account.

I sent initaial email with digital signautre from my private email to my company email, and imported it in Address book with private email public key (I use Outlook 2k3, IE6 and XP at company, and Outlook 2k7, IE7 and XP at home)

In company I installed your root certificates as trusted (AAA, UTN-USERFirst-ClientAuthenticationandEmail,…)

Now goes strange issue:

  1. If I send email from private email to company email just with digital signature - I got meesage that digital signature is not trusted or invalid.

  2. If I send email from private email to company email with digital signature and encrypted (with company email public keys) - everything is ok.
    Digital signature is presented as trusted and valid. Encryption is also fine.

  3. If I encrypt email from company account and send it to private account - everything is also ok.

What could be issue?

Thanks!