Do not accept timestamps from the future

src/mimeparser.rs

@@ -35,6 +35,7 @@ use crate::param::{Param, Params};
 use crate::peerstate::Peerstate;
 use crate::simplify::{simplify, SimplifiedText};
 use crate::sync::SyncItems;
+use crate::tools::time;
 use crate::tools::{
     get_filemeta, parse_receive_headers, smeared_time, truncate_msg_text, validate_id,
 };
@@ -1864,10 +1865,12 @@ impl MimeMessage {
     ///
     /// Returns `None` if there is no such header.
     pub async fn chat_group_member_timestamps(&self) -> Option<Vec<i64>> {
+        let now = time();
         self.get_header(HeaderDef::ChatGroupMemberTimestamps)
             .map(|h| {
                 h.split_ascii_whitespace()
                     .filter_map(|ts| ts.parse::<i64>().ok())
+                    .map(|ts| std::cmp::min(now, ts))
                     .collect()
             })
     }