Well, (sigh) if I am to be scolded for one lapse from the honest path, I had better post my responses to some multiple points in one fell swoop.

1. I don't necessarily speak in sentences. Or post in sentences or write in sentences. The letters I (used to, before email!) write to friends had more dashes than a year of athletic meets. I speak / write in units of thought. Unfortunately, my units of thought are not always crystal clear to those around me....

2. >I am surprised by how "Australian" the people who left the UK in adulthood sound - perhaps to real Australians they still sound very British. I wonder whether it is because the rhythm of Australian accents are quite "catchy". I think there is a similar phenomenon in New Zealand.<

I think this is because an accent has at least two distinct constituents - the pronunciation of individual words and the intonation of sentences or stretches of speech. I have frequently been told I sound Australian because of a rising tone at the end of many of my phrases. I have frequently been told I sound English because of my pronunciation of specific words.
I have also been told (by Mormon missionaries in Japan) that I sounded 'Austrian, no German, no Dutch, no Danish, er maybe Australian?' Given that I am a native English speaker who at that time had never been near Australia, I don't know whether to be amused or enraged! So I settle, most of the time, for bewildered.

3. As for long emails, fine in social circles. In business, if it's going to be long, nine times out of ten it would be better as an attachment. Attachments get less mangled in formatting by electronic transmission - they don't lose bolding, italics, tabs etc, or gain line breaks and little >>> which can make things extremely tedious to read. Only today I got a reply to an email with 'my comments added in bold' - except that all the text had defaulted to plain courier. Had to print it out and read every line to get the three comments that had been added...
Grrrr...

PS see what I mean about incomplete sentences? But I'd NEVER put them in formal business writing!