Yes, 'no doubt' ('probably') means you assume that something is true or likely to happen - it sounds like 'I suppose', for example, 'No doubt Expector will give us another blog challenge soon.'
If you want to say something is certainly or definitely true, you use 'there is no doubt that'. You can say 'There is no doubt that your English has improved.'
You can also use 'without (any) doubt' ('absoulately certain') to emphasize that something is true, for example, 'MyEC is without doubt the best En