Starting Sentences with the Word "so"

[Deb]

I seem to start a new sentence with the word "so". Here's an example:

Their PO box is no long in service. So, any and all mail will go to their street address.

Searching the internet, it's not wrong. There is reasons not to use it. A comma isn't needed, but Outlook strongly suggested it with those grammar lines under the word.

I suppose I could just leave it off. But, but I'm just wondering if there's something else I could use or what others think.

For shorthand reference, I could only find the word "also", but I've always wrote the word 'so' with the last 's-o' symbols.

[lvw]

I''m not quite sure what you mean. But "so" should not be written like the last syllable of "also". Instead, it should be written with the righthand (clockwise) s, not with the lefthand s of "also". That is, it should look more like f-o than like p-o.

[phoenix]

Maybe alternatives can be "thus" or "therefore" or "accordingly".

Their PO box is no longer in service. Thus, any and all mail will go to their street address.
Their PO box is no longer in service. Therefore, any and all mail will go to their street address.
Their PO box is no longer in service. Accordingly, any and all mail will go to their street address.

Or maybe rewrite the sentence.

All their mail will go to their street address because their PO box is no longer in service.