You have NOT provided anything but a partial greeting string from the server you are connecting to.

There is something wrong with your settings but without the full log it is not possible to know what.

My internet hosting company has been taken over by another one. The log-in data remained the same, but since that day, the following occurs while sending mails:

a) when I send Emails with my Default identity  (Pegaus-Menu: Tools | Identities... ), it works fine.

b) But sending (single) mails with another indentity (e.g. my wife's) any outgoing mail is rejected while sending.

The message from the server is:
-------------------------------------------------------------------------------------------------------------------
:
:
0075 220-We do not authorize the use of this system to transport unsolicited,
0025 220 and/or bulk e-mail.
:
:
-------------------------------------------------------------------------------------------------------------------

Analysing the whole error log, the support of the hosting provider says that Pegasus wants to send emails using another IP address than the IP address of my PC.
My router / small home network works on DHCP.

Does Pegaus store / cache IP addresses anywhere?

> My internet hosting company has been taken over by another one. The log-in data remained the same, but since that day, the following
> occurs while sending mails:
>
> a) when I send Emails with my Default identity  (Pegaus-Menu: Tools | Identities... ), it works fine.
>
> b) But sending (single) mails with another indentity (e.g. my wife's) any outgoing mail is rejected while sending.
>
> The message from the server is:
> -------------------------------------------------------------------------------------------------------------------
> :
> :
> 0075 220-We do not authorize the use of this system to transport unsolicited,
> 0025 220 and/or bulk e-mail.
> :
> :

There is no error message, you really should provide a session log (munging the password) so we can tell what the server is complaining about.

> -------------------------------------------------------------------------------------------------------------------

> Analysing the whole error log, the support of the hosting provider says that Pegasus wants to send emails using another IP address than
> the IP address of my PC.
>
> My router / small home network works on DHCP.
>
> Does Pegaus store / cache IP addresses anywhere?

Nope and the server connecting IP address should be the IP address of the router.

Having provided the log to Thomas, his key answer was/is:

An identity has their own POP3/SMTP and personal settings.
You have to become that identity and then make sure that the settings are all the same as for the default setting.

( In the other identities was an old/wrong entry in the SMTP part. )