Old question - but I forgot the answer - when does tar pitting kick in

[#1]

The reason for this is that I may need to send emails to our local membership - over 650 at the last count - and I will do this by exporting the relevant membership file in Excel as csv and then importing into Outlook (not the free one)
There are a couple of options for sending then (all using BCC)
Blocks of 50 or some other number which won't hit the spam filter
All at once accepting that it may take a few hours to send
If sent as blocks how long should I allow between blocks
Note that the email will include a couple of url links to websitesand I don't want to be identified as a spammer by the automatic systems

[#2]

Tar-pitting isn't really applicable these days. Rather than throttle connections, you're much more likely to find our servers rejecting your attempts to send email if you exceed the limits that are imposed. These limits differ (and are subject to variation over time) depending on what platform you're using to send messages (Webmail or client), and where you're sending your messages from (Plusnet connection, non-Plusnet connection, within the UK, overseas etc.).
Assuming you're using your Plusnet connection, then last time I checked you are limited to 1000 recipients per hour and a maximum of 250 recipients per email.
Hope that helps.

[#3]

Thanks Bob
It does indeed - looks like three batches or four to be safe then