while ((line = file.ReadLine()) != null)
            {
                string messageDownloadID = line ;
                if (String.IsNullOrEmpty(messageDownloadID))
                {
                    continue;
                }
            }

while(condition) {
    statement
    continue
    statement
}

top:
while(condition) {
    statement
    goto top;
    statement
}

for (int i = 0; i < 10; i++) {
    if (i == 5) {
        continue;
    }
    Console.WriteLine(i);
}

int j = 0;
while (j < 10) {
   if (j == 5) {
      continue;
   }
   Console.WriteLine(j);
   j++;

while ((line = file.ReadLine()) != null) {
    string messageDownloadID = line;
    if (String.IsNullOrEmpty(messageDownloadID)) {
        continue;
    }
}

while ((line = file.ReadLine()) != null) {
    string messageDownloadID = line;
    if (String.IsNullOrEmpty(messageDownloadID)) {
        continue;
    }
    ProcessMessageDownloadID(messageDownloadID);
}