Slow receiving speeds is usually a symptom of interference- electrical noise from some on-board equipment creating interference with your radio receiver. Common culprits are shore-power battery-chargers (yours or a marina neighbors, or running from a genset), also some AC inverters (especially small ones often used to power computers), also some 12v fridge units (e.g. Adler Barber, Frigiboat), some 12v florescent lighting, some instrument systems, etc. This is a general radio problem, not particular to Sailmail or email.
Clues that this is a problem include continuous or periodic tones or squealing or chirping over a wide range of frequencies, or simply a higher-than-normal level of static or “hiss”. The radio’s signal-strength indicator may also show a higher signal level than expected for a quiet channel- the M710 should no signal-strength bars when listening to a quiet channel above 8 megs, and perhaps 1 or possibly 2 bars on lower frequencies.
Isolating receiver noise requires a bit of rigorous testing, don’t try to shortcut this. When underway or in a quiet anchorage (and away from marinas and power lines), turn off everything except the radio (everything!). Then find a weak-but-clear radio station (e.g. WWV on 5 or 10 megs, or a shortwave broadcast station). Then listen carefully while you turn on each circuit one at a time. If the station disappears under static, or you hear suddenly hear beeps or squeals, then you found a source of interference- turn off that circuit and continue, there may be more source of interference.
Depending on what you find, it may be possible to filter the offending equipment but the short-term fix is to make sure that circuit is turned off when using the radio. The biggest problems are often in marinas, where noisy battery chargers can wipe out radio reception for a whole dock or the entire marina. Short of pulling the main breaker, there is no easy solution. Fortunately most marinas also offer some sort of wireless internet connection. There is information here on how to connect to Sailmail directly via internet.
Also check the antenna and ground connections carefully, a corroded connection can cause problems for both sending and receiving. It is a good idea to disassemble, clean and reconnect the antenna and ground connections at least once a year, especially in the tropics.
And of course pay attention to Airmail’s propagation window, make sure your lat-lon is up to date and select times and frequencies which are well within the “green” zone.
Good luck and good sailing,
Jim & Sue