Learn English – I was going to say

He was going for a morning walk every day.

He would go for a morning walk every day.

Both the sentences are grammatical, but there's a difference between their meanings.

The first sentence is in the past continuous. You can use this tense to refer to something that you did again and again in the past. The sentence means that he used to go for a morning walk again and again every day. The sentence is grammatical though it's odd or unusual. You usually go once, not several times, for a morning walk every day.

You can use would instead of "used to" to refer to something that you did regularly or habitually in the past. The sentence is quite clear. It was his habit or routine to go for a morning walk every day; of course, it conveys the sense of going for a walk once, not several times, every day.

The sentence you received with I was talking about is perfectly idiomatic. The past continuous there refers obliquely to your earlier conversation in which he described the problem. It bears the added nuance that now you have in hand something which will help you to understand my earlier words more completely.

As you say, "phoned ... then he sent me an email".

Compared to the simple past told, the continuous was telling puts a little extra emphasis on the durational act of telling, as distinct from an incident without duration. Thus, it might be paraphrased "as I assume you do remember from our recent conversation, which should not yet have shrunk down to a mere dot in your mind" as might well happen with the passage of time. With time, you might remember only that you two had spoken but not the conversation.

The continuous implies that the speaker fully expects this matter to be fresh in your mind. He expects you to remember the conversation. For that reason, the simple past is not better.