Thanks, Brian. Now I understand. In summary:
In the toolbar above the folder list there is button which toggles between "Preview" and "List" display. When Preview display is enabled, the Folders menu has an item "Preview Mode" (P Mode). When P Mode is enabled, messages are previewed in a pane below the folder list; when disabled, the text "Message preview is disabled" appears in that pane instead.
P Mode is enabled by default when Pegasus opens in Preview display, or when it opens in List display then toggled to Preview. Once P Mode is disabled, it remembers that state when toggling between Preview and List display, but only for that session; when Pegasus is restarted, it again defaults to P Mode enabled.
Large messages will not open for me with double-click _whenever P Mode is enabled_; they do open with double-click when P Mode is disabled, and they always open by clicking the Open button on the Attachments tab, regardless of the P Mode setting. I don't know the lower size limit for what makes a "large" message -- a 2.3 Mb message opened but 6.1 Mb would not.
These particular messages contain multiple attachments; the largest was a 3.3 Mb PDF file, and it could be opened by double-clicking it.
(And FWIW, I think it's unnecessarily confusing to be in "Preview" yet able to toggle "Preview mode" while remaining in "Preview." The terms are almost identical yet control different functions.)
<p>Thanks, Brian. Now I understand. In summary:</p><p>In the toolbar above the folder list there is button which toggles between&nbsp;<span style="font-size: 10pt;">"Preview" and "List" display.&nbsp;</span><span style="font-size: 10pt;">W</span><span style="font-size: 10pt;">hen Preview display is enabled, the Folders menu has an item "Preview Mode" (P Mode).&nbsp;</span><span style="font-size: 13.3333px;">When P Mode is enabled, messages are previewed in a pane below the folder list; when disabled, the text "Message preview is disabled" appears in that pane instead.</span></p><p><span style="font-size: 10pt;">P Mode is enabled by default when Pegasus opens in Preview display, or when it opens in List display then toggled to Preview. Once P Mode is disabled, it remembers that state when toggling between Preview and List display, but only for that session; when Pegasus is restarted, it again defaults to P Mode enabled.</span></p><p><span style="font-size: 10pt;">Large messages will not open for me with double-click _whenever P Mode is enabled_; they do open with double-click when P Mode is disabled, and they always open by clicking the Open button on the Attachments tab, regardless of the P Mode setting.&nbsp;</span><span style="font-size: 13.3333px;">I don't know the lower size limit for what makes a "large" message -- a 2.3 Mb message opened but 6.1 Mb would not.&nbsp;</span></p><p><span style="font-size: 10pt;">These particular messages contain multiple attachments; the largest was a 3.3 Mb PDF file, and it could be opened by double-clicking it.</span></p><p>(And FWIW, I think it's unnecessarily confusing to be in "Preview" yet able to toggle "Preview mode" while remaining in "Preview." The terms are almost identical yet control different functions.)</p>