when received on mail.ru it gives the following error in styles:
<p class="pc-cont-italic" style="margin-top: 1px; margin-bottom: 1px; color: black; font-family: Helvetica, Arial, sans-serif; font-weight: normal; text-align: left; line-height: 1.3; font-size: 16px; display: block; letter-spacing: -0.5px; font-style: italic;padding: 0;" align="left">Региональный менеджер</p> If a paragraph has a margin-top property: 1px; That property works - there is no error. As soon as I supplement the paragraph with the property margin-bottom: 1px; This error pops up.
Where to dig, tell me, please?

msoprefix has properties that only Outlook understands. Well, maybe another word. But no one except the office suite will understand it, so it is naturally crossed out as an unknown property. UPDATE: Re-read the question, changed my mind so to answer. - Qwertiy ♦