This advice from VeryBritishProblems may sound a bit peevish at first, but for tea, the microwave is very uneven. You’re likely to find the first sip warm, and then drink it faster only to discover the middle scalding. Best to boil new water and brew another tea bag for evenness. One thing I learned from Douglas Adams’s advice on the perfect cup of tea is to boil the water, fill your mug, and pour it out. Then refill the mug with the boiled water and a tea bag. Let it steep. This will warm the cup and keep your tea warmer longer. I’ve tried this method and it really is perfect.
We also invested in an electric kettle. It is very fast and does a great job, and by invest, we paid about $25, so it easily pays for itself if you start brewing your tea at home.