How one should link to pages that are outside the current domain?

Do, i simply make them target="_blank" and give them a different background color or add some icon to them to differentiate them from rest of the links that point to internal pages..?? - This one seems to be the most recommended but what about target="_blank"..

Or i should open an internal pop-up..??

Or i should avoid links to external domains..??

In addition, if i have same information under contact us, about us, etc. links on two different domains then should i replicate that information on both the domains or i should link to it in one of the above ways or in some other better way on one of the domains..??

I have followed this post and this one but still am not sure how this thing needs to get addressed..

How one should link to pages that are outside the current domain?

Do, i simply make them target="_blank" and give them a different background color or add some icon to them to differentiate them from rest of the links that point to internal pages..?? - This one seems to be the most recommended but what about target="_blank"..

Or i should open an internal pop-up..??

Or i should avoid links to external domains..??

In addition, if i have same information under contact us, about us, etc. links on two different domains then should i replicate that information on both the domains or i should link to it in one of the above ways or in some other better way on one of the domains..??

I have followed this post and this one but still am not sure how this thing needs to get addressed..