Well, there are all these races, right? They all share noticable similarities as to the aspect of human lower and upper bodies. Assuming all (playable) races in TES share the same sixual reproductive organs, how are their relationships looked upon by other denizens of Nirn?

In Morrowind, there was a side-quest where an Imperial woman on the side of the road asks you to give her glove to a Dunmer man, as a sign of her affection. The player's journal mentions nothing about how this is looked upon by society. There is also the option to be Ahsanni's "special friend".

In our (earth) history, there are of course interracial relationships, however, everyone has different opinions on them. (I'm not trying to be racist)

So my question is...how does Tamriellic society treat interracial relationships? If anyone can answer, it would be interesting to hear.

Tamrielic society is a vast number of distinct and differing societies, cultural mores and attitudes, and values, and no sweeping statements can be made to include all of them. Many are even diametrically opposed to each other.

In general, they seem pretty liberal about the subject though; it's barely even addressed at all. There are many examples of accepted interracial couples, even amongst the Imperial family.
One might expect the Altmer to dislike the idea, however.

In the Septim Empire there was a Dunmer empress, I cannot remember since it's been awhile since I played to whom she was married. If homes can be burglarized by generic NPC's this time around face it, youd much rather have a nordic or redguard wife holding order to your abode while your away saving the world from Dragons or out earning your keep. They never said marriages where 100% based on romance, for all you know you could strike a deal with a Khajiit woman who's a thief that she'll find and steal things and split the loot with you if you marry her to keep her from having suitors from bothering her. Essentially marriages may not mean romance in this game at all, they could have function to them other than being a diversion.

There seems to be very little racism in the :tes: universe other than a few remarks from disgruntled workers. So I doubt anyone will be shouting, "Tonight, you yiff in hell!"

Someone didn't play Morrowind

Racism however is very prominent, the Nords hate Elves because their elves, the Dunmer feel superior to the beast races and enslave them and like most evles feel better than everyone else, the Altmer feel their superior to everyone, the Ra'gada (Redgaurd's) the same, the only race that doesn't harbor blantat racist elements are the Imperials and Bretons, and perhaps the beast races. In general however, racism is everywhere, though its not featured heavily in game as it is in lore.

I played Morrowind. I never finished it and didn't talk to many people however. The feeling superior and the enslaving isn't really racism, just [censored]ry.

Yeah....that not correct.

Other than what Lord Tidus said:

• The orcs have been subjected to genocidal attempts against them by the Redguards, Bretons, and Tiber Septim since they became orcs, and only ended when they had the Numidium.
  
• The sload unleashed a plague that kill off most of the population of Tamriel, and ended up being blown to hell
  
• The nords killed off the falmer, and would do the same to the Altmer. Then again, this goes way back during the Dawn.
  
• The altmer believe themselves to be the direct offspring of the gods, and that man, on a whole, needs to be removed completely, along with Talos. I'd expect the dunmer to get the same treatment, due to being complete and utter heretics and vile perversions of what mer are. Reason being also stems from the same reason nords hate mer, though with not as much kill every single elf ever. The nords got a bit soft. Also, the altmer on the mainland are not even considered altmer to their Summerset brethren. They are just that bad.
  
• The dunmer of Morrowind (particularly the Temple, Cammon Tong, Indoril, and Dres) believe themselves to be superior, and everyone else is nothing more than mongrel dogs, and therefore, deserved to be treated like mongrel dogs. They, on a whole, held no care about who they enslaved, for everyone was inferior to them. It took an imperialized dunmer king (Helseth) to put a stop on it, as Helseth was raised primarily by bretons. This is especially why they are extremely pissed about being in the empire. To them, they have been taken over by a bunch of backwater barbarians.

In general, expect the citizens of Tamriel to be xenophobic, and will hate something instantly if it's different. There are differences amongst individuals, but the races on a whole are quite xenophobic, with the Imperials being the least racist and xenophobic.

I was just joking good sir about not playing Morrowind.

Aye, Hellmouth gave a more in depth explanation here. Racism can be found on every corner of Tamriel.

I edited it a bit, adding more with the dunmer and extra fluff.

About the Nords killing the Falmer, it was because they were hunted by them. When the Nords came to Skyrim, the Falmer thought that they were trying to take over their province, so they tried killing them, but then the Folks from up north kicked their asses.

Anyways, racism is clearly prominent in Tamriel, but I still can't find a definitive answer to my question.

Well, I know in Anvil, anyone that mentions that one nord's wife is a bosmer, they keep saying they'd rather marry a horse. So...I guess in certain groups and cultures, it's frowned upon, if not openly against the mere thought.

I can bet you the altmer of Summerset Ilse would never even dream of marrying someone less than themselves. The Imperials, I'd assume, to be more accepting of it. Nord and dunmer coupling does seem to happen, though not sure if it's through less than ideal intentions. I can see the khajiit just never giving a crap, as they almost always never seem to give a [censored] about anything. With argonians my current guess is it depends if you're part of the hardcoe Black Marsh party or not, though I doubt viable offspring will be produced.

I think the answer to your question lies in parallels to our own world. In certain cultures/group it will be looked down upon, and other it won't, just like in our world.

I'd say see which races that race x hates, likes, and is indifferent to, and base assumptions on that. It's all we really have anyway.

There is Oblivion dialog related to an Imperial/Dunmer coupling in Chorrol. Pretty much what you would expect from Americans in the 1970s.

Come to think of it, Oblivion's Cyrodiil pretty much was America with a different backdrop.

Katariah.
Barenziah is also a notable example of an Imperial/Dunmer relationship.

Despite the prominence of xenophobia and racial hatred, interracialism really does seem to be a well-accepted thing.

I know, haha, I guess I just never really paid much attention to the racism.