Must the QQ-plot line be at a 45 degree angle? A qq-plot for a regression I ran looks like this:

My understanding was always that there should be a 45 degree angle, i.e. from approx bottom left to top right corner. Must that really be the case? Or is the following QQ-plot fine and normality can +- be assumed (apart from the heavy tails).
Feedback would be greatly appreciated!

If the residuals are Normal, the points on the QQ plot should closely follow the line. For the most part ($|r_i| < 2$) the point are close to the dotted line.
As you said, the tails are heavy. These tails are very heavy. If we had a one or two residuals that were a little bit to big (say not much more than $\pm 3$) I would usually say that its 'Normal enough'. Here you have quite a lot of $|r_i| > 3$ and one that looks to be as big as $9$? The probability of observing a standardised residual larger as $9$ under a standard normal is $\approx 10^{-19}$. This suggests that there is a very serious discrepancy between your model and the data. There are also lots of other large outliers in your data so I would be very worried about how well it generalises to the real world.
