Why isn't mail drop working?

Thanks for the reply and sorry for the delay in replying.

First, I can't use AirDrop from my iPhone XS to my Mac - this is explained in one of the articles you linked, which says the earliest Mac one can use for AirDrop is:

• "Mac from 2012 or later (excluding the mid-2012 Mac Pro) using OS X Yosemite or later"

My Mac is a mid-2011 iMac, running High Sierra (the most recent allowable version of Mac OS available on this model), so doesn't qualify. Although the AirDrop window opens when chosen in the Finder, it doesn't work. I think it would be more helpful if Apple either indicated this in the window or removed the AirDrop option, but anyway that's the position.

Following your advice, I sent the email with the photos using mail drop to another address (a gmail one that I own) from my iPhone. I was asked the size to choose. I chose a small size, as this was an experiment - the total was about 600Kb. I clicked on Send. Sure enough it worked! However, encouraged by that I did it again choosing a large size, similar to my actual requirement so that the total amount sent was around 2Mb. This took a long time to arrive (I suppose it had to be uploaded to iCloud and then downloaded into my iMac) but it did work! So the trick is not to send the email to one's normal email address, or indeed an alias of the address, which is what I actually did.

So, great! You solved my problem. Thanks very much.

Sadly, I spoke too soon. After my good experiences of mail drop, described earlier, I sent a really large chunk of photos - about 50Mb. The email was accepted by the iPhone, and the preparation done, then apparently sent, but it never arrived, even after several hours (about 14 at the last count). So there is some hidden restriction on volumes, or something like that. To put it in context, there is enough room in my iCloud storage and on my iMac to accommodate the pictures, and my internet connection was open throughout and capable of delivering streaming video, for example. I have absolutely no idea what the restriction is or why it went wrong. I suppose I should approach Apple Support directly. Annoying.

Thanks so much for staying with me, Eric.

Sorry, but I don't completely understand the question.

I did send the email to myself. In order to avoid an apparent issue (already discussed) when one sends from and to the same account, I sent the mail to a gmail account I have. As described above, this worked twice, but it broke when I sent a really large set of photos. I see that gmail might have rejected it. but I see no sign that it was ever sent, either in the IN box on my Mac or on the Google Mail site accessed via a browser.

Despite my doubts about sending from and to the same address, I just tried it. I am using Apple servers, since this is an IMAP account with an icloud.com address. I just tried to do this, with a message size of about 50Mb, via mail drop. As before everything appeared to go well at the iPhone end, but there was no sign of the mail being received. I then looked in the Outbox of my iPhone's email client, and sure enough the unsuccessful mails (the new one sent to my .icloud address and the old one sent to my gmail one) are there - apparently the mail drop process hasn't started. I don't know if there is any way to make it do so. I am even more puzzled than before!