Nelleke wrote:

I don't have problems with receiving mails, but after sending mails I
get the message:

"554 5.7.0 Reject, id=16822-12 - Message refused, this message
appears to be spam"

Without the headers to inspect, no one can determine if you got this
NDR (non-delivery report) e-mail from your own sending mail server or
from the recipient's receiving mail server.

Your sending server doesn't like your e-mail because it looks spammy.
Contact your e-mail provider on why their outgoing spam filter
triggered on your message. Or, and probably more likely, the
recipient's receiving mail server doesn't like e-mails from you or your
sending mail server. The content of your e-mail is too spammy, or you
or your sending mail server have been flagged in a blacklist as a spam
source. From the NDR message, my guess is that the content of your
e-mail was seen as too spammy.

In the menu options/preference/junkmail, I unticked the box about
postmarking message, I entered the mail addresses on the Safe Senders
List and Safe Recipients List and altered the preferences in my
AntiVirus Program. I didn't help. What else can I do?

The recipient's receiving mail server is probably the one complaining
about the content of your e-mails. Nothing you are configuring in
Outlook is going to affect how someone's mail server handles your
message - until you figure out what it is in your message that they
don't like. Safe Senders/Recipients has nothing to do with the
*content* of your message that someone ELSE sees.

Altered the preferences in your AV program tells no one ELSE just
exactly what you did. Even you can see that is a vague and worthless
statement to someone ELSE.

How many e-mails did you send to the same domain? Are they mostly
compromised of your signature and very little real content? Do you use
templates to boilerplate your e-mails? If you send tons of e-mails of
nearly identical content (signature or template) then the receiving
mail server sees you spamming their customers with a flood of identical
e-mails (i.e., you are bulk sending the SAME content). You never
mentioned how many e-mails per day you are sending to the same domain
and just WHAT is contained in your messages.